This newsletter is going to highlight activities associated with the Transportation Research Board’s ADK70 Standing Committee on Geospatial Data Acquisition Technologies. This committee is concerned with applications of high-accuracy geospatial data acquisition technologies in support of the digital infrastructure for the design and construction of transportation facilities. Members have various backgrounds and expertise and are located in different regions of the United States.

The committee holds two meetings a year, one at the January TRB Annual Meeting held in Washington, D.C., and a summer meeting in different locations each year in late July.

This year, the meeting of the Geospatial Acquisition Technologies in Design and Construction Summer Committee was held on July 29-31, 2024, in Washington, D.C. Topics included new technologies on data collection, modeling and plan delivery. There were updates from organizations such as the National Geodetic Survey, the Federal Highway Administration, the American Association of State Highway and Transportation Officials and various state departments of transportation on technology, standards, specifications and industry needs. See the agenda below.

I first got involved with this committee in 1999, when I worked for NGS. One may ask, why would a geodesist be interested in a committee that focuses on the design and construction of transportation facilities? In my opinion, this is an important committee that addresses geospatial issues that affect all users of geospatial data, not just state Department of Transportation (DOT) surveyors and engineers.

As anyone who has been reading my GPS World Survey Scene newsletters knows, I remind everyone that “geodesy is the foundation for all geospatial products and services.” As previously stated, this committee is concerned with applications of high-accuracy geospatial data acquisition; therefore, surveyors and geodesists must be involved to address issues associated with positioning. Anyone using or acquiring geospatial data should be interested in this committee’s activities.

During AKD70 summer workshop meetings, participants talk with technical experts about the latest advancements in geospatial data acquisition technologies. I would encourage anyone interested in high-accuracy geospatial data acquisition technologies to learn more about this TRB committee, which is currently chaired by Wei Johnson, South Carolina DOT.

Digital delivery geometric consistency concerns

One session at the meeting discussed concerns with digital delivery geometric consistency. We now live in a world where everything is digital. Today, most surveying and mapping instruments collect and generate data in digital format. This paradigm has affected how surveyors, geodesists, and engineers provide their products and services. So, what is the issue with digital delivery geometric consistency?

As I previously stated, I am a geodesist, so I think in geodetic coordinates (latitude, longitude, ellipsoid and orthometric height) or cartesian coordinates (X, Y and Z).

Three-Dimensional Positioning (XYZ). (Photo: NGS)

Orthometric, Ellipsoid and Geoid Heights from NOAA Technical Memorandum NOS NGS 59. (Photo: NGS)

Looking at the diagram in the above image, I would like to highlight that the orthometric height is measured from the geoid along a curved line. The curved line is based on an infinite number of geopotential level surfaces that exist between the geoid, which is a geopotential surface, and the mark located on Earth’s surface. This is why gravity plays a part in determining the orthometric height of a mark.

This means that leveling height differences are not the same as ellipsoid height differences. To compute a GNSS-derived orthometric height, a geoid height is subtracted from the GNSS-derived ellipsoid height. This is only an approximation because of how the two heights are measured but, at this moment, it is accurate enough for surveying and mapping applications.

What about computing an ellipsoid height from an orthometric height? The ellipsoid height can be computed using the equation h = H + N (ellipsoid height = orthometric height + geoid height). Once you have an ellipsoid height, you can compute the X, Y, and Z coordinates of the mark. Orthometric heights derived from leveling data are one-dimensional (orthometric height only), whereas GNSS-derived coordinates are three-dimensional (XYZ or latitude, longitude, ellipsoid height). Therefore, to compute a cartesian coordinate (XYZ), from a leveling-derived height users must generate a latitude and longitude of the mark. It is important to use the appropriate geoid height and to record that information in a metadata file.

NGS has developed web-based applications to convert coordinates between different coordinate systems and transform between different reference frames and/or datums. See the box titled “NGS NCAT Web Tool.” I described the NCAT web tool in my October 2019 and September 2023 GPS World newsletters.

NGS NCAT web tool. (Photo: NGS)

Photo: NGS

So, from a geodesist’s point of view, there is no issue with digital delivery geometric consistency if the appropriate tools are correctly used to convert coordinates between different coordinate systems and transform them between different reference frames and/or datums. That said, unique coordinate systems may be used by engineers to create 2D and 3D as-built drawings, such as blueprints and models. This should not be a problem for developing a transformation model if the appropriate information is available.

The AutoCAD Map 3D website states that users can combine data from maps using different coordinate systems (see the box titled “Excerpt from AutoCAD Map 3D Site”).  The site states that “AutoCAD Map 3D toolset automatically converts them to the coordinate system of the current drawing.”  This is an indication that CAD routines are working on handling different coordinate systems.

That said, users should make sure that the conversions and transformations are using the correct formulas and parameters. For example, I would like to know what defines the Latitude-Longitude 84 coordinate system that is highlighted in the box. I am not suggesting that anything is incorrect in the definition of the coordinate system. I am just saying that I do not know what the statement means; I would need more information before I can use the data.

Excerpt from AutoCAD Map 3D 2025 site.

That said, ESRI and Autodesk, two industry leaders, have created a partnership to integrate GIS and Building Information Models (BIM), which seeks to create an integrated and collaborative workflow that connects data sources. ESRI denotes this as ArcGIS GeoBIM.

Representatives from ESRI and Autodesk participated in the meeting. During the meeting, Linda Foster, ESRI and President-Elect of the National Society of Professional Surveyors (NSPS), gave a presentation that included a discussion of the ArcGIS GeoBIM web-based tool. Linda highlighted how geodesy and surveying provide the foundation for Digital Twin products. Her presentation included a diagram that I have recreated below.

Notice that geodesy is at the base and digital twin is at the top of the inverted triangle. See the box titled “Geodesy Provides the Foundation for all Geospatial Products and Services.” The diagram is like the one I highlighted in my February 2022 GPS World Newsletter to emphasize the geodesy crisis. Both diagrams emphasize the importance of geodesy and surveying in creating geospatial products and services. It is encouraging to see that ESRI and Autodesk are working together to understand the needs of both communities. This will lead to the development of an improved system.

Image: Dave Zilkoski — based on Linda Foster’s presentation at the TRB AKD70 summer meeting on July 30, 2024.

From a geodesist’s viewpoint, there does not seem to be a problem with digital delivery geometric consistency. Of course, I know that it is not as simple as I am making it. I realize that the “devil is in the details,” which means that something that appears to be simple will identify issues that will have to be dealt with during development and implementation. During the meeting, it was announced that the TRB AKD70 Committee is developing a webinar titled “Resolving ambiguities between 3D virtual models and the real world” to make people aware of the issues.

Proposed Webinar

Proposed title: “Resolving ambiguities between 3D virtual models and the real world”
Proposed description: The transportation industry is rapidly moving towards achieving digital product delivery and digital as-built objectives in the Civil Infrastructure sector. They are doing this by adopting a 100% end-to-end digital, asset-centric, interoperable data flow. However, the current methodologies being discussed use outdated concepts that rely on 2D/1D plans and profile/cross-section sheets as part of physical construction reality. These methodologies are not in line with current construction objectives, which require the use of Open BIM and Digital Twin concepts. Therefore, it’s crucial to address the current geospatial and geodesic ambiguity between the real world and BIM (virtual 3D models) to ensure a clear understanding of the proposed solution and its efficient implementation. This is especially important considering the industry’s reliance on Global Navigation Satellite System (GNSS) measurement methodologies. There is an imperative need to resolve this geospatial and geodesic ambiguity by adopting sound geodetic methodologies. The webinar will present the basic tenets of geodetic engineering from three points of view: the Department of Transportation (DOT) perspective, the digital product delivery perspective and the Survey/Geodesy perspective.
Proposed purpose: To raise awareness among the DOT community, which is intent on achieving the 100% digital end-to-end asset-centric interoperable flow objectives, of the need to resolve the ambiguities between virtual 3D models and the real world.

I always learn something new at these meetings and continue to build new relationships expanding my professional network. These meetings are open to anyone, so I would encourage everyone to learn more about the TRB ADK70 Standing Committee on Geospatial Data Acquisition Technologies. Please contact Wei Johnson for more information about getting involved with the committee.

<p>The post TRB ADK70 Standing Committee on Geospatial Data Acquisition Technologies summer meeting first appeared on GPS World.</p>

Photo: SonjaBK / iStock / Getty Images Plus / Getty Images

In my last newsletter, I highlighted the release of a beta version of a new NOAA CORS Network (NCN) Station Web Page. As demonstrated in my newsletter, each CORS in the NCN has its own page with data, metadata, maps and photos for that station displayed in a modular layout so information is easily found all in one location. This past month, I had the privilege of participating in a meeting with representatives from the American Association for Geodetic Surveying (AAGS), the National Society of Professional Surveyors (NSPS) and the National Geodetic Survey (NGS). As a Past President of AAGS and the current Chair of the AAGS Membership Committee, I participate in these quarterly meetings.

AAGS aims to lead the community of geodetic, surveying, and land information data users through the 21^st century. AAGS members develop new educational programs, including presentations, seminars, and workshops on topics related to geodetic surveying; and articles and papers that inform the membership of the latest scientific and technological developments and how to implement them in the most cost-effective and efficient manner.

In my previous newsletters, I have reminded everyone that time is running out to obtain a working knowledge of the new, modernized National Spatial Reference System (NSRS). The release of the new, modernized NSRS is only about a year away. As of July 2024, NGS plans to have a beta version of the new, modernized NSRS available around the summer of 2025 for users to test and evaluate new products and services. After enough testing has been performed, the new, modernized NSRS will be officially published – probably in early to mid-2026.

At the meeting, NGS highlighted some new products on its Alpha Preliminary Products site. The alpha site provides products that are useful for individuals who want to obtain a better understanding of the products that will be distributed as part of the new, modernized NSRS.

Some of my previous newsletters have discussed the Alpha product concept.  My September 2023 newsletter highlighted the first two Alpha products; that is, State Plane Coordinate System of 2022 (SPCS2022) and NGS Coordinate Conversion and Transformation Tool (NCAT).  As of June 2024, two more products have been added to the Alpha Preliminary Products site – “GEOID2022 Alpha” and “Alpha Values for EPP.”  The State Plane Coordinate System of 2022 (SPCS2022) is probably the most important to land surveyors.  There are significant changes between the SPCS2022 and the State Plane Coordinate System of 1983 (SPCS83). I will highlight the latest options in the alpha site later in this newsletter.

First, I want to bring attention to the importance of ensuring that the state’s legislation is modified or rewritten, if required, to include that the current horizontal and vertical datums are being replaced with the new, modernized NSRS. The “Learn More” button on the SPCS2022 Alpha site provides information about legislation.

On the “Learn More” site, NGS provides an SPCS legislation template.

Per personal communication with Michael Dennis, Ph.D., NGS SPCS2022 Manager, as of June 26, 2024, the following 12 states have have enacted into law NSRS modernization: Alaska, Idaho, Iowa, Kansas, Kentucky, Louisiana, Nebraska, North Carolina, South Dakota, Vermont, Washington, and Wyoming.

Users can download examples of actual new state legislation here.

Examples of legislation.

During the joint AAGS/NSPS/NGS meeting, Tim Birch, the executive director of NSPS, said that anyone who has questions about updating legislation for the new, modernized NSRS, including SPCS2022, can contact him directly. NSPS has experience working with agencies and individuals to develop legislation as indicated in the following statement on the NSPS website.

“We are the voice of the professional surveying community in the US and its territories. Through its affiliation agreements with the respective state surveying societies, NSPS has a strong constituency base through which it communicates directly with lawmakers, agencies, & regulators at both the national and state level. NSPS monitors and comments on legislation, regulation, & policies that have potential impact on the activities of its members and their clients, and collaborates with a multitude of other organizations within the geospatial community on issues of mutual interest.”

Tim’s contact information is provided on the NSPS home webpage: Staff List – National Society of Professional Surveyors (nsps.us.com).

As previously stated, the two latest alpha products are the “GEOID2022 Alpha” and “Alpha Values for EPP.” My December 2017 newsletter discussed GEOID 2022 and the North American-Pacific Geopotential Datum of 2022 (NAPGD2022), and my February 2022 newsletter discussed the Euler Pole Parameters process and use in the new, modernized NSRS.

The GEOID2022 Alpha page provides a version of GEOID2022, which is the most recent prototype of the geoid models. The reference ellipsoid is Geodetic Reference System 1980 (GRS 80, but the geometric reference frame is ITRF2020). The Alpha GEOID2022 prototype data is available for download in two formats, “ASCII” and “.b.” There is a static component (SGEOID2022) and a dynamic component (DGEOID2022). These grids will be useful to programmers who want to develop and test their systems. Additional grids and tools will be available in the future.

Technical Details of the Alpha prototype of GEOID2022

GEOID2022 alpha is the last prototype of GEOID2022. It covers three regions: the North America–Pacific region, Guam and Northern Mariana Islands, and American Samoa. The spatial resolution of the geoid model is 1 arcminute. The geoid heights, which are in the tide-free system, are with respect to the reference ellipsoid of the Geodetic Reference System 1980 (GRS80) in the ITRF2020 geometric reference frame. GEOID2022 alpha includes static and dynamic components for the geoid heights. For detailed fundamental parameters of the geoid model, refer to NOAA Technical Report 78.

GEOID2022 Alpha

The Alpha EPP site provides the Euler Pole Parameters (EPP) that are needed to define the relationship between the ITRF2020 and models on the North America, Caribbean, Pacific and Mariana plates as discussed in NGS’s Blueprint Part 1 document.

Alpha Values for EPP

As stated in Blueprint Part 1, NGS will define the official relationship between ITRF2020 and the four NSRS TRFs through equation 59, using the rotation matrix in equation 58 resulting in equation 60.

I programmed this using a simple Excel spreadsheet to compute some of the potential changes between epochs for North Carolina. They were very similar to the ones that I depicted in my February 2022 newsletter that discussed the Euler Pole Parameters process and provided plots depicting the movement.

I would like to highlight the latest information available on the State Plane Coordinate System of 2022 alpha site. As previously stated, in about a year, the new, modernized NSRS will be available as a beta product. Users must get prepared by accessing NGS’s alpha products as well as taking the opportunity to provide feedback to NGS to improve their products and services. The Online Interactive Maps page provides information about the zones for every U.S. state and territory.

Clicking on the Online Interactive Maps link opens a NOAA ArcGIS online website that provides information about the Alpha State Plane Coordinate System 2022 preliminary zone designs. I have highlighted a few items that may be of interest to users.

The site provides a description of the site, links to various types of zones, links to data sources and information about distortion.

SPCS2022 online interactive maps.

Clicking on the link for zone definitions provides a list of zones and their parameters. This same information is also provided when users click on a zone on the map. I will demonstrate this later in this newsletter.

Per personal communication with Dennis, as of June 26, 2024, seven states have some or all their SPCS2022 zone definitions formally finalized, consisting of 205 out of the 965 zones (the total number of zones is still preliminary):

• Alaska (partial coverage multizone layer)
• Arizona (both multizone layers)
• Idaho (both multizone and statewide)
• Kentucky (both multizone and statewide)
• North Carolina (statewide zone; it has no other zones)
• South Dakota (both multizone and statewide)
• Wisconsin (multizone)

Dennis informed me that the information on the alpha SPCS2022 Experience has been updated. He told me that the total number of zones decreased from 967 to 965, but based on coordination with the International Association of Oil & Gas Producers (IOGP) Geodesy Subcommittee the number may eventually increase to 972 (more about that in a future newsletter).

He stated that his goal is to finalize the zone definitions by the end of this calendar year or early 2025. Users should keep checking the alpha site.

Dennis mentioned that the website now offers a new feature that provides the distortion value when users click on the map. A nice thing about that is the site can be used on a smartphone, allowing users to obtain real-time distortion information from their location.

Clicking on the link titled “View” in the upper right corner of the box brings up a map that depicts the SPCS2022 zones.

View of ALPHA (preliminary) SPCS2022 zone designs.

When you click on the note about the ALPHA being preliminary, the map underneath appears where the user can select the type of maps they wish to review.

The following options are available: All Zone Layers, Statewide Zone Layers, Multizone Complete Layers, Multizone Partial Layers, and Special Use Zone Layers.

Users can use their mouses or the “+” button on the left-hand side” to zoom to a particular region, or use the search button on the right-hand side to select a State or zone.

Using the search box.

Information about a particular zone pops up by clicking on a point on the map.

Detailed information provided for a zone.

Each zone provides links to other features based on the location of the point selected on the map.

The image below provides the distortion in ppm for the point selected on the map.

The Alpha NCAT site can be used to obtain an estimate of the changes between SPCS83 and SPCS2022. It should be noted that all values will be in meters (m) and international feet (ft).

International feet may be new to some surveyors who were previously using the U.S. survey feet in SPCS83. The U.S. survey foot will not be used with the NSRS, including SPCS2022 coordinates. NGS and the National Institute of Standards and Technology (NIST) have taken action to deprecate the U.S. survey foot. What does that mean?. NIST has the following statement on its website: “Beginning on January 1, 2023, the U.S. survey foot should be avoided, except for historic and legacy applications, and has been superseded by the international foot.” This means that NGS will not be publishing SPCS2022 in U.S. survey feet but all historic products and services such as SPCS83 will still be provided in U.S. survey feet (sft) and international feet (ift).

More information and resources about the deprecation of the sft are listed below (personal communication from Dennis):

• The official announcement is the final determinationFederal Register Notice (FRN) on deprecation of the sft issued on 10/5/2020. It was jointly issued by the National Institute of Standards and Technology (NIST) and NGS. I encourage everyone concerned about this topic to read it closely and in its entirety; it can likely answer most questions. The FRN includes information on the continued use of sft for legacy applications (such as SPCS 83). That is stated in the last paragraph of the “Notice of Final Determination” section; in items #1 and #2 in the “Counterpoints to Feedback Expressing Opposition”section; and in the second paragraph of the “Implementation Summary and Actions” section.
• The legacy issue is also addressed in the 10th FAQon the NIST website and in the 11th FAQon our “new datums” FAQs web page.
• The 40 states that officially adopted the sft for SPCS 83 are listed in Table C.1 of Appendix C of NOAA Special Publication NOS NGS 13, “The State Plane Coordinate System History, Policy, and Future Directions.”
• Although the final determination FRN is itself not a law, Congress has passed several laws giving NIST the authority to maintain national standards of measurement. These and other related federal laws are given in the initial sft FRNissued on 10/17/2019.
• An NGS webinar given on 11/10/2022 addresses the deprecation of the sft in the context of state plane. Two previous NGS webinars also provide additional background and historical information on the sft, one given on 4/25/2019 and the other on 12/12/2019.

Input to Alpha NCAT.

Photo:Output from Alpha NCAT.

This newsletter highlighted the products on NGS’s Alpha Preliminary Products site. The alpha site provides products that can be useful for individuals to obtain a better understanding of the products that will be distributed as part of the new, modernized National Spatial Reference System (NSRS). NGS is providing these products on an alpha site so that they can get feedback from users. I would encourage all users to access the alpha sites and provide comments to NGS so that their products and services better meet the needs of the surveying and mapping community.

Alpha Preliminary Products

Welcome to the NGS National Spatial Reference System (NSRS) Modernization Alpha Product Release Site. This site provides examples of the content, format, and structure of data and products that NGS plans to release as a part of the Modernized NSRS.

Products found on this page are for illustrative purposes only and do not contain any authoritative NGS data or tools. They are under active development and are subject to change without notice.

To provide feedback on any of the content on this site, please email ngs.feedback@noaa.gov.

<p>The post NGS new alpha preliminary products in support of the modernized NSRS first appeared on GPS World.</p>

I mentioned in the May 2024 newsletter that NGS announced the release of a beta version of a new NOAA CORS Network (NCN) Station Web Page. Each CORS station in the NCN will have its own page with data, metadata, maps and photos displayed in a modular layout so information is easily found in one location. This newsletter will describe some features of the new beta site.

The beta site is located here.

I will highlight some of the information provided by the routine, but I would encourage others to access the beta site and provide feedback to NGS. NGS states on the site that “This is a Beta product. We are interested in your feedback. Please email us at: ngs.feedback@noaa.gov and indicate the subject as “NCN Station Pages Feedback.”

When you access the website, it defaults to the CORS station GODE. The user has the option to enter their own CORS station in the box located on the right-hand side of the webpage.

Texas CORS Station TXLV.

A nice feature of the site is that the CORS data availability for the last seven days is provided under the Station Information section. For those interested in downloading data, there is a button titled “Quick Data Download,” on the top left corner. The site allows users to download daily data from the past 30, seven or two days.

In my example, I downloaded the last seven days of data for CORS TXLV. It only took a few seconds to download and provide the data in a zipped file. If a user includes this process in their standard operating procedure, they can easily download all the CORS data required for their project.

Downloading TXLV GNSS data.

Another planning tool available is the weather information for a week. Today, most users can get the weather information on their phone. However, this is a convenient option to have when you are looking at available CORS on the day of occupying marks. It can help in managing schedule changes.

There is an option to show the five nearest CORS relative to your selected CORS by clicking on the button titled “Show Closest 5 on Map.”

CORS Located near TXLV.

Clicking on the button labeled “Show Legend” provides information about the CORS depicted on the map. This is a useful feature especially if selecting CORS that provide GNSS data other than GPS and/or data at different sampling rates.

If a user clicks on the button “Open NGS Map,” the site will access the NGS Map website and provide information about the selected CORS. This allows users to get information about the CORS. I found that the beta site provided most of the same information using the various options on the NGS Map website.

NGS Map depicting CORS TXLV.

The site provides photos and equipment history that may help in troubleshooting an issue associated with processing sessions or during the analysis of the adjustment results. I have highlighted that a new antenna was installed at the TXLV CORS on August 5, 2021. I will explain later in this newsletter how this information helped me during my analysis of a GNSS project.

Photos and equipment history of TXLV.

Under the Coordinates and Velocities section, the site provides information about the latest coordinates and velocities along with superseded values for the selected CORS. The superseded values may not be of interest to most users, but I am always looking at the changes in CORS coordinates. It is my nature to try to understand the reason why something has changed; especially for CORS that I am including in a GNSS project.

Coordinates and velocities.

Clicking on the link titled “Position and Velocity” under the Coordinates and Velocities section provides the coordinate and velocity information for your selected CORS. I have highlighted the ITRF2014 velocities, the NAD 83 (2011) velocities, the latest antenna type, installation date and the dates the positions and velocities were revised.

As shown in the image above, the position and velocity sheet provide the dates that the position was revised. Clicking on the link titled “Datasheet with GRP/MON included (if available)” in the Coordinates and Velocities section provides the datasheet that lists the NAD 83 (2011) superseded survey control values. The superseded ellipsoid heights from the datasheet are provided in the box titled “Excerpt from TXLV Datasheet.”

When you are trying to estimate heights to the 2 cm level, changes in published NAD 83 (2011) CORS heights at the 2 cm level are significant and should be investigated and understood. This beta CORS website offers useful information that can help understand some of these changes. I will explain later in the newsletter how this information and other data from the beta site helped me in the analysis of my GNSS project.

Excerpt from TXLV data sheet.

The beta site provides plots that depict the daily positions and residuals for a CORS. In my May 2024 newsletter, I stated that NGS has developed a Beta CORS Time Series Tool that provides information that assists users in selecting appropriate CORS for a project. The Beta CORS Time Series Tool provides the residual differences from the daily NGS OPUS-NET solutions with the coordinates from the official CORS’ coordinate functions. The excerpt below explains the plots and residuals:

NCN Residual Time Series Comparison Tool (NCN PloTS)

This tool computes and displays the residuals for up to 50 CORS stations within the NCN. The mean, standard deviation, and root-mean-square error of the residuals are also provided in a summary table that is available for download. This tool is informational, not authoritative.

The residuals are calculated as the difference between the daily observation at a station and the official daily coordinates for a station. The daily observation is processed from the GPS L1 and L2 signals only, using a network adjustment program. There must be a minimum of 8 hours of data present in a 24 hour file for a solution to be generated. The network adjustment program is an internal application developed by NGS for monitoring the position of the CORS stations in the NCN (Gillins et al., 2019). The official daily coordinates for a station are calculated using the reference epoch (2010.0) position and velocity published as the station coordinate function in the Position and Velocity File. An example of a Position and Velocity File for NCN station GODE can be found here. To obtain Position and Velocity Files for NCN stations please visit the NCN Station Pages and navigate to the Coordinates and Velocities section.

This tool is optimized for plotting data extending between 30 to 90 days in length but can be customized to other time frames. The earliest start date currently available is October 27, 2018, which is the completion date of the MYCS2 and the end date can be as recent as 3 days before the present day. This three-day time lag is so that the final orbits can be used in the network adjustment to create the daily solutions. Then, please enter the 4-character station ID for at least one and up to 50 CORS stations in the NCN and submit this request to obtain a map, summary table of comparative statistics, and residual plots during the date range.

The beta NGS NCN station pages show similar plots to the Beta CORS Time Series Tool. the station pages also allow users to create position and residual plots at different periods. I find these plots very useful when selecting CORS to be included in a GNSS project. The latest plots are of interest to users when selecting CORS to be included in their GNSS project but there are reasons to look at plots depicting older time periods.

Position and residual plots for TXLV.

I previously mentioned that the antenna of CORS TXLV was changed on August 5, 2021, so I used the option to plot the last five years to include data before and after the date the antenna was changed. I highlighted August 7, 2021, on both plots. This was two days after the antenna was changed on CORS TXLV.

There appears to be a 2 cm upward shift in the up component after the new antenna was installed. There was also a change of about 1 cm in the north component. Something else to notice in the position plot is that the east component has a significant tilt during the five years. The below provides the ITRF2014 velocities — the eastward component velocity is —1.21 cm/year. In 5 years, one could expect to see about a 6 cm change.

Position and residual plots for TXLV.

Five-year position plot of TXLV.

Five-year residual plot of TXLV.

Position plot of TXLV for selected time interval.

These small changes affected my analysis and network adjustment results. During the past several years, I have participated in several Harris-Galveston Subsidence District (HGSD) GNSS projects performed in the Houston-Galveston, Texas, region. I have been involved with estimating subsidence in the Houston-Galveston, Texas, region for about 40 years so when I see changes in height values indicating an apparent uplift it makes me question my results. Therefore, I started investigating the CORS involved in the GNSS project. I looked at the Texas CORS surrounding the GNSS project: WHARTON CORS, COLUMBUS CORS, HEMPSTEAD CORS, LIVINGSTON CORS, and LIBERTY CORS.

The table below provides the differences between the published ellipsoid height and the previous superseded height for the five CORS. As the table indicates, the published ellipsoid height of the CORS increased by about 2 cm from the superseded height. This led me to use the NGS NCN Station Pages to investigate these CORSs. I found that all five of these CORSs had new antennas installed in 2021 and their position plots depicted a similar shift.

I want to emphasis that I am not saying that anyone did anything wrong or incorrect.  The CORS manager of these sites provided the appropriate metadata to the NGS CORS team so the site information could be updated and correctly reported. What this indicates to me is that the installation of the new antenna and setup may have affected the height component of these CORS, that is, it may have changed the official position of the monument’s reference point. Again, I want to emphasize that I am not saying that anyone did anything wrong or incorrect.  NGS’s process includes monitoring all CORS that are part of the NOAA CORS Network (NCN). The NGS CORS Team noticed the significant change in the up component comparing it to its expected value, so they computed a new coordinate and published the new coordinate in 2022. In my opinion, anyone using these CORSs as constraints in their GNSS projects after the date that the new antenna was installed and before the new coordinate was published could have generated adjusted heights that are in error by 2 cm. As previously stated, when you are estimating heights to the 2 cm level, changes in published NAD 83 (2011) CORS heights at the 2 cm level are significant. In my opinion, this type of analysis should be performed by all users that are incorporating CORS in their GNSS processing.

Keep checking NGS beta site because NGS makes changes based on user feedback. As I previously stated, I would encourage everyone to access the beta site and provide your feedback to NGS. NGS states on the site that “This is a Beta product. We are interested in your feedback. Please email us at: ngs.feedback@noaa.gov and indicate the subject as “NCN Station Pages Feedback.”  I have talked to the CORS team and they really would like feedback. The team will make changes to the website based on feedback from users.

<p>The post NGS beta version of a new NOAA CORS Network station web page first appeared on GPS World.</p>

Photo: Dana Caccamise II

In my November 2023 GPS World newsletter, I highlighted the announcement made by the National Geodetic Survey (NGS) of the recipients of the National Oceanic and Atmospheric Administration (NOAA) FY 23 Geospatial Modeling Competition awards. The primary objectives of these projects are to modernize geodetic tools and models and to develop a geodetic workforce for the future. My last three GPS World newsletters — February 2024, March 2024 and April 2024 — highlighted three of the grantees, Scripps Institution of Oceanography, The Ohio State University, and Oregon State University that included developing models to address what NGS denotes as the Intra-Frame Deformation Model (IFDM) and creating geodesy curriculums that will help address the geodesy crisis. Changes in these geomatic programs will provide students with the skills in geospatial systems that will make available opportunities for employment in the public and private sectors. This newsletter will address the proposal by the fourth NGS geospatial modeling grant awardee, Michigan State University (MSU).

First, it should be noted that this award is denoted as the MSU geospatial modeling award; that said, the execution of the project will be led by MSU, along with two sub-awardees — University of Alaska Fairbanks (UAF) and Michigan Tech University (MTU). Jeffrey Freymueller and Julie Elliott are the MSU grant’s principal investigators (PI). They provided me with information about the goals and objectives of their grant proposal.

The MSU proposal includes enhancing software and monitoring capabilities for NGS, enhancing graduate-level geodetic education and providing opportunities for graduate and undergraduate students to be exposed to geodetic science. Again, focusing on geodesy curriculums will help address the geodesy crisis and will provide students with the skills in geospatial systems that will increase their opportunities for employment in the public and private sectors. The proposal has two main goals and objectives.

Goals and objectives

CORS Dashboard 

• Build an online, web-based CORS dashboard that will support monitoring of the continuously operating reference station (CORS) network.
• Making it easier to continually validate the current position of CORS sites to the existing motion models (IFDM).
• To validate and correct the motion models themselves in the presence of time-dependent tectonic and volcanic activity.

Education

• Work with partner universities toward developing and establishing a consortium model for future distributed geodetic degree programs that leverage the capabilities and capacity of multiple universities.
• Develop new course material for graduate level geodetic education that is intended for hybrid or asynchronous remote delivery and the establishment of a formal degree program.
• Host summer undergraduate interns who will work on a variety of geodetic projects including the CORS dashboard.
• Two graduate students will be supported to work on various aspects of the proposed work at MSU and MTU.

Anyone using NGS’s “user-friendly” software knows that they are working on improving their web-based services. However, NGS still needs help from outside users.

I want to emphasize that I am not criticizing NGS’s products and services. I worked for NGS for over three decades, and I personally know that NGS has limited resources to accomplish too many tasks. NGS needs to focus on the science and get help with the development of models, tools and the dissemination of results and data. That is one of the reasons that these geospatial modeling grants are important to all users of the National Spatial Reference System (NSRS).

The proposed CORS Dashboard will be very useful to NGS employees monitoring the CORS and evaluating the IFDM. The proposal highlights that users of NGS products and services have various precision and accuracy requirements and that all users expect that NGS products will be sufficiently precise and accurate to meet their positioning needs. Their design of the CORS Dashboard will provide a tool for effectively monitoring and assessing a CORS site status and the validity of its coordinates. The first phase of this tool is being developed for internal use at NGS. However, in my opinion, after all the bugs have been identified and dealt with, NGS will release a version for the user.

Not all CORS are created equal. So, having a CORS Dashboard that quickly identifies and notifies CORS users of a systematic deviation at a site, regardless of cause, will avoid promulgating erroneous positions to users. In addition, providing statistical information about a CORS site such as short- and long-term plots and their residuals would provide users with helpful information for planning a GNSS project. The metadata of CORS is extremely important since most of the CORS included in the NOAA CORS Network are not maintained by NGS.

CORS managers are supposed to notify NGS when they make any change to their CORS site such as an antenna change and any changes surrounding the CORS site, including new vegetation or construction that could cause potential obstructions. The CORS Dashboard will help identify issues with CORS before users include them in their projects.

NGS’s OPUS Project online user guide provides information on selecting the best CORS.  The following is from the user guide:

• Using the centered time-series plots, select the candidates with RMS (in northing, easting, and up) less than 2 cm. Candidates with large spikes, data gaps or discontinuities should be rejected. Selecting candidates in this manner will provide some assurance that the published coordinates and velocities at the CORS agree with the daily solutions for the CORS.
• The best CORSs should have “consistent” data depicted in 90-day short-term time-series plots. NGS processes each day of GNSS data collected at each CORS and plots the differences between the resulting coordinates and the published coordinates on short-term time-series plots (in terms of delta northing, easting, and up). These plots can be accessed for every CORS at https://geodesy.noaa.gov/corsdata/Plots/. CORS with plots that depict significant biases from the published coordinates (more than 2 cm in northing, easting, or more than 4 cm), spikes or data gaps should be avoided.

NGS has developed a Beta CORS Time Series Tool that provides information that assists users in the selection of appropriate CORS for a project. The tool computes and displays the residual differences from the daily NGS OPUS-NET solutions with the coordinates from the official CORS’ coordinate functions. The tool also generates a summary table with the mean, standard deviation, and root-mean-square error of the residuals. On April 24, 2024, NGS announced the release of a beta version of a new NOAA CORS Network (NCN) Station Web Page. According to the announcement, each CORS in the NCN will have its own page with data, metadata, maps and photos for that station displayed in a modular layout so information is easily found all in one location. I will describe this new beta site in a future newsletter.

The new, modernized NSRS will offer time-dependent coordinates based on an IFDM. This has been described in previous GPS World newsletters (February 2022 and August 2022). The MSU proposal includes developing a model that accounts for crustal movements — such as earthquakes, slow slip events, and volcanic eruptions, — as well as slower, cumulative growth of error due to post-seismic deformation, surface loading (ice or water changes) and changes in rates of human-induced subsidence due to fluid withdrawal. Like any model, the IFDM model will have uncertainties. Being able to provide a realistic estimate of the uncertainties of the IFDM is very important. The PIs of the proposal have extensive knowledge and experience in generating models and uncertainties. As noted in their proposal, the “problem” may not be an issue with the site or the equipment but with the model. See the box titled “Excerpt from the MSU Proposal.”  I have highlighted several sections that I believe are important to the users of the new, modernized NSRS.

As anyone who has been following my newsletters knows, I have been highlighting the geodesy crisis and programs that advance the science of geodesy — July 2020, November 2022, and December 2022. The proposal includes developing geodetic science courses that will be optimized for hybrid or asynchronous online courses that address advanced technical topics on GNSS, InSAR, map projections, reference frames, and adjustment theory. This will build on existing programs at MSU, UAF and MTU that will provide an online graduate degree in geodesy. MSU envisions this to be a step toward a consortium-based enhanced graduate-level education that provides a range of course options and flexibility. The university believes that there will be opportunities to expand the consortium in the future. The courses have not been finalized yet,  but below are some of the topics and concepts that are being considered for the program.

As previously stated, these courses have not been finalized. An important aspect of the courses is that they contain content that will provide students with the skills and knowledge in geodetic concepts to help address the geodesy crisis in the United States.

I first mentioned the need for more trained geodesists in my July 2020 article for the “First Fix” column of GPS World, where I stated that the shortage of U.S.-trained geodesists poses a significant economic risk for the United States. In that column, I mentioned how geodetic science and technology now underpin many sciences, large areas of engineering such as driverless vehicles, UAVs, navigation, precision agriculture, smart cities and location-based services.

My November 2022 GPS World Newsletter highlighted “The inverted geospatial pyramid” graphic, which depicts how the entire $1 trillion geospatial economy is supported and dependent on geodesy. A lack of geodetic expertise in the United States presents a significant challenge, with future impacts on positioning, navigation, mapping and dependent geospatial technologies. These changes in the geomatic programs at the universities being funded by NGS’s geospatial modeling grants will provide students with the skills in geodetic concepts that will provide opportunities for employment in the public and private sectors involved with geospatial technology.

This newsletter and my past three GPS World newsletters highlighted the four NGS Geospatial Modeling grantees, which included creating geodesy curriculums that will help address the geodesy crisis. The MSU proposal describes a consortium-based enhanced graduate-level education program that will provide a range of course options and flexibility. I believe their proposed hybrid or asynchronous online program will provide more opportunities for individuals to study geodesy and advance the science of geodesy.

One final note about the NGS Geospatial Modeling Grants. On June 4, 2024, Brad Kearse, director of NGS, will moderate a session at the UESI Surveying and Geomatics 2024 Conference held in Corvallis, Oregon, on June 4 to 5, 2024. This will be a good opportunity for participants to obtain a better understanding of the geospatial modeling grants.

Lunch & panel discussion: NGS Geospatial Modeling Grants panel session

Moderator: Brad Kearse, Acting Director, NGS

The NGS Geospatial Modeling grant program is focused on modernizing and improving the National Spatial Reference System (NSRS) and address emerging research problems in the field of geodesy. A secondary objective of this funding opportunity is to support a geodesy community of practice in collaboration with federal and nonfederal stakeholders to address the nationwide deficiency of geodesists and improve the coordination and use of geospatial data. This panel session will explore the research and other activities underway from recipients of the most recent round of the NGS Geospatial Modeling Grant Program.

<p>The post MSU developing CORS dashboard and geodetic program first appeared on GPS World.</p>

Image: NGS website

As the announcement stated, NGS is in the process of compiling, organizing, and cleaning all the relevant GNSS and leveling data contained within the NGS Integrated Database and the OPUS shared solutions database for preparation of the new, modernized NSRS. The data will be used in national scale survey adjustments using NGS’ new software package called LASER (Least-squares Adjustments: Statistics, Estimates, and Residuals). The adjustments will compute the initial sets of geometric and orthometric reference epoch coordinates (RECs) on many existing survey control marks and CORS around the country. The definitions of RECs and survey epoch coordinates (SECs) are spelled out in NOAA Technical Report NOS NGS 67, NGS’s Blueprint Part 3. My April 2021 GPS World newsletter highlighted the Blueprint Part 3 document, and my August 2022 GPS World newsletter provided details on RECs and SECs. Using the results of the adjustments, NGS will produce a suite of models and tools that will enable users to access and work within the Modernized NSRS.

During the last several years, NGS’ GPS on Benchmarks program has been encouraging stakeholders and partners around the country to submit GNSS data to NGS on marks that they use. This will ensure that these marks will have updated RECs when the new system is implemented. Also, just as important, marks that also have North American Vertical Datum of 1988 (NAVD 88) heights will be used to improve the local accuracy of the NAVD 88-to-NAPGD 2022 transformation tool.

NGS’ plans include accepting user data, but after February 29, 2024, they will not include additional GNSS and leveling data for the initial REC national adjustment and for use in building the transformation tools. In 2018, I wrote a series of GPS World newsletters that highlighted NGS’ GPS on BM program (February 2018, April 2018, June 2018, and August 2018). At that time, the GPS on BM program was very useful in the development and implementation of the hybrid geoid model GEOID18. This newsletter will provide an update on the GPS on BM Transformation Program and provide some advice on strategically selecting marks to improve the local accuracy of the NAVD 88-to-NAPGD 2022 transformation tool.

Links to the GPSonBM Transformation Tool web map and GPSonBM Progress Dashboard are provided in NGS’ announcement. As the announcement states, the GPSonBM Transformation Web Map provides information on marks that have GNSS-derived ellipsoid heights and published NAVD 88 orthometric heights, and where there are still gaps.

When users click the link GPSonBM Transformation Tool Web Map, they are connected to a web map depicting a prioritized list of marks where new GNSS observations would be most helpful to the development of the transformation model between the current vertical datum (e.g., NAVD 88) and the modernized NSRS.

NGS’ prioritized list of benchmarks are labeled as Priority A or B. Clicking on the “About” button on the webpage provides information about the priority marks. See the boxes titled “GPSonBM Transformation Tool Web Map” and “Excerpt of Information on Priority A and B Marks.”

GPS on BM Transformation Tool Web Map. (Image: NGS website)

To assist users in their selection of marks, NGS developed criteria based on spatial resolution factors. See the box titled “Excerpt of Information on Spatial Resolution Factors.” As previously stated, time is running out. In my opinion, users should prioritize their GPS on BM plans based on the NGS’ criteria. I have highlighted what is important for users to consider when selecting marks.

Many areas across the country do not have benchmarks at the 10 km spacing, so there are some areas without any hexagons or marks. As stated in the spatial resolution factors, NGS will interpolate over any areas with no GPS on benchmarks. In areas that have gaps larger than 10 km, that is, that are missing hexagons, I would recommend occupying several marks in each hexagon surrounding the gap to ensure that marks with valid NAVD 88 heights are part of the transformation tool. The web tool defaults to the Denver, Colorado, region when you access it but users can drag the map to an area of their interest or select a location.

Locating marks using the GPSonBM transformation tool web map. (Image: NGS Website)

Acquiring data in mountainous regions and areas that have large distances between completed hexagons is probably the most important for users to focus on. The box titled “Locating Marks Using the GPS on BM Transformation Tool Web Map” provide marks that need to be observed.  As an example, I have highlighted two areas that have large distances between benchmarks and completed hexagons.  In this case, it would be important to occupy a couple of marks in the highlighted locations. Clicking on a mark provides a box with the following information: Mark Priority, Population Priority, PID, Designation, Stamping, State, County, Stability code, Last Date of Recovery, Last Date of Observation, Link to NGS Datasheet, and a Link to a Shared Solution (if one exists).

Clicking the link titled “More Info” next to Datasheet brings up the NGS datasheet for the mark, and clicking the link titled “More Info” next to Shared Solution” brings up the Shared Solution information (see the boxes titled “Mark Priority Information for Mark G 80,” “Excerpt from NGS Datasheet for Mark G 80,” and “Shared Solution for Mark G 80.”). I would recommend that State surveying organizations (and surveyors) perform this type of analysis and strategically occupy marks that fill in important gaps. There is less than two months remaining to submit data to NGS that will support the transformation tool. 

Excerpt from NGS datasheet for Mark G 80. (Image: NGS website)

Shared solution for Mark G 80. (Image: NGS website)

The GPSonBM Progress Dashboard illustrates the progress that each state and territory has made toward NGS’ goal of 10 km (and 2 km) data spacing nationwide.

GPSonBM Program Dashboard. (Image: NGS website)

Users can see the GPS on Benchmark information for a particular state by clicking on the name of the state on the left side of the website.

Selection of North Carolina. (Image: NGS website)

I highlighted North Carolina because I live in that state. The map informs the users of how many 10 km priority A (89) and B (32) marks are remaining to be occupied, and the percentage completed (92%). Clicking on the link “To see remaining marks to be collected use GTT Web Map App,” located under the map, depicts the remaining marks to be collected. As you can see from the plot, North Carolina has several marks in the eastern portion of the state that still need to be occupied with GNSS.

Status of GPS on benchmarks in North Carolina. (Image: NGS website)

A nice feature of the map is the legend and layer list buttons. Also, information about the mark appears if you click on a mark.

Example of legend and layer list. (Image: NGS website)

The image below provides a list of layers that can be selected using the webtool.

The following image depicts marks that have been completed. As you see from the plot, North Carolina has been very active in the GPS on Benchmark program.

Completed marks in North Carolina. (Image: NGS website)

Users can also click on the button to see which 10 km (and 2 km) hexagons have been completed (see the boxes titled “Completed 10 km Hexagons in North Carolina” and “Completed 2 km Hexagons in North Carolina”).

Completed 10km Hexagons in North Carolina. (Image: NGS website)

Completed 2km Hexagons in North Carolina. (mage: NGS website)

The North Carolina Geodetic Survey, under the leadership of Gary Thomson, along with NC surveyors has been involved with the GPSonBM program from its inception.

As previously stated, the website provides the list of priority benchmarks and the status of GPS on Benchmark for each state. There are other states that have been very active in the GPS on Benchmark program such as Minnesota and Wisconsin.

Completed 10 km Hexagons in Great Lakes Region. (Image: NGS website)

The following images provide the GPS on Benchmark information for West Virginia.

Status of GPS on benchmarks in West Virginia. (Image: NGS website)

Completed marks in West Virginia. (NGS website)

Completed 10 km hexagons in West Virginia. (Image: NGS)

The following image provides a plot of an area in West Virigina that highlights a region with a large gap between completed 10 km hexagons. If a user was interested in supporting the development of the transformation model in West Virigina, occupying a mark with GNSS in this area would help improve the local accuracy of the NAVD 88-to-NAPGD 2022 transformation tool.

Overlay of completed and status of benchmarks in West Virginia. (Image: NGS website)

North Carolina and West Virginia are not large states compared to some western states. The boxes titled “Status of GPS on Benchmarks in Colorado,” “Completed Marks in Colorado,” “Completed 10 km Hexagons in Colorado,” and “Overlay of Completed and Status of Benchmarks in Colorado” provide the information for Colorado. Looking at the plots there appears to be many regions that could use GPS on Benchmark occupations.

Status of GPS on benchmarks in Colorado. (Image: NGS website)

Completed marks in Colorado. (Image: NGS)

Completed 10 km hexagons in Colorado. (Image: NGS website)

Looking at the plot in the image below, there appear to be many marks that were occupied in populated areas such as Denver, Fort Collins, and Colorado Springs. The marks along the southern border were part of NGS’ 2017 Geoid Slope Validation Survey (GSVS) Project. The area highlighted by the orange box is an area that is lacking GPS on Benchmark occupations. The distance between the nearest completed 10 km hexagon is 60 kilometers. In other words, the two completed hexagons are more than 120 km apart. As previously stated, NGS will interpolate over any areas with no GPS on benchmarks.

Overlay of completed and status of benchmarks in Colorado. (Image: NGS website)

Again, in areas that have gaps larger than 10 km with missing hexagons, I recommend occupying several marks in each hexagon surrounding the gap to ensure that marks with valid NAVD 88 heights are part of the transformation tool. To demonstrate this concept, I have selected an area in Colorado near benchmark U 153 (PID LN0062).

Benchmark U 153 in Colorado. (Image: NGS website)

The following image depicts the locations of the completed hexagons near benchmark U 153.

NGS has developed web tools to assist users in the selection of marks for the program. Two web tools that I find useful are the Leveling Project Page and the Passive Mark Page. The Leveling Project Page provides information on leveling line data. Users can find information about the marks involved with a certain leveling line. There are links to the Passive Mark Page and NGS datasheets on the Leveling Project Page. My October 2020 GPS World newsletter described the Passive Mark Page web tool in more detail, and my June 2021 GPS World newsletter demonstrated the use of the tools.

In this example, I selected U 153 because it was located between two completed 10 km hexagons that are 125 km apart. That said, looking at the information from the passive mark web tool, it appears that the published height of the benchmark is based on 1934 leveling data. That by itself is not a bad thing but the Orthometric Height Residual is very large (-23.1 cm). This implies that the difference between the GNSS-derived orthometric height using Geoid18 and the published NAVD 88 height disagreed by 23.1cm. This could be due to the movement of the mark and, in my opinion, is not a good candidate for the transformation tool.

As previously stated, NGS’ Leveling Project Page, provides information on the benchmarks and associated data involved in a leveling line. See the box titled “Excerpt from NGS Leveling Project Page for L2577.” Users can find information about all the marks involved with a certain leveling line.

Excerpt from NGS Leveling Project page for L2577. (Image: NGS website)

Distance between 10km hexagons near B 383 in Colorado. (Image: NGS website)

Again, I used the Passive Mark tool to find detailed information about the mark. See the box titled “Excerpt from NGS Passive Mark Tool for B 383.” This mark was last leveled in 1966 and the Orthometric Height Residual is small (1.2 cm). This implies that the difference between the GNSS-derived orthometric height using Geoid18 and the published NAVD 88 height disagreed by 1.2 cm.

This could be a good candidate for the GPS on BM program and the transformation tool.

Excerpt from NGS passive mark tool for B 383. (Image: NGS)

For completeness, I looked at another mark in the same area.

Distance Between 10km hexagons near B 154 in Colorado. (Image: NGS website)

I highlighted this mark because it was last leveled on the same 1934 leveling line as mark U 153. Unlike U 153, looking at the information provided by the Passive Mark tool for B 154 indicates that the GNSS-derived orthometric height agrees with the published leveling-derived orthometric height. The orthometric height residual is only -2.1 cm. This would be another good candidate to fill the area between the two completed hexagons.

This newsletter provided some advice on strategically selecting marks to improve the local accuracy of the NAVD 88-to-NAPGD 2022 transformation tool. Again, I would recommend that state surveying organizations and surveyors perform the analysis described above and strategically occupy marks that fill in important gaps. There is less than two months remaining to submit data to NGS that will support the transformation tool.

NGS has developed web tools such as Passive Mark Page and Leveling Project Page to assist users in identifying marks for inclusion in the development of the transformation model between the current vertical datums (e.g., NAVD 88) and the modernized NSRS.

<p>The post Time is running out to submit GNSS or leveling data for initial NSRS modernization first appeared on GPS World.</p>

Maps have existed for centuries. The lines on maps indicating the boundaries of political and administrative units — cities, counties, states, and countries — are graphic representations of the limits of those entities. These lines don’t, however, typically exist in real life. There isn’t a large line between the United States and Canada stretching from the Pacific Ocean, through the Great Lakes, and onto the Atlantic Ocean.

The same goes for latitude and longitude lines on maps and globes. The public generally accepts the various delineations on maps as being somewhat accurate with an unwritten level of trust in those who have produced these maps.

Definition

trust: assured reliance on the character, ability, strength, or truth of someone or something.

Here are the guidelines surveyors use for determining surveys.

1. lines physically verified in the field and proven from evidence
2. monuments and/or boundaries set and called for within legal descriptions
   • natural monuments
   • artificial monuments
3. adjoiners (to determine junior/senior rights)
4. courses
   • bearings, then distances (metes and bounds states)
   • distances, then bearings (public land survey states)
5. recitation of area
   • controlling description
   • evidentiary description
6. coordinates: local and/or geodetic

Surveyors rely on physical monuments, title documents and evidence of occupation to assist with the establishment of not just major dividing lines, but all lines of property, public or private. Finding, setting and honoring physical monuments has been a significant character trait of the surveyor for as long as maps have existed.

Monuments are placed to determine the endpoints of these lines as depicted on maps or plats, but what happens when technology introduces new ways to re-establish these lines? What will happen to our monuments when technology — more specifically those who utilize them — deems them obsolete?

The guidelines above are known as “priority of calls” or “rules of construction” by the surveying community. These items have provided the instructions for surveyors to follow in retracement of lines for many years. However, like nearly everything else in our modern world, technology has a hand in modernizing even this time-honored “surveyor’s code of retracement.”

Who would have guessed that the rotary phone dial would give way to touch-tone buttons, that the system would jump from landlines to cellular and satellite signals to remote handsets, then progress to receivers evolving away from physical buttons to touchscreens?

Technology changes the rules of the game, and surveying may be more in its crosshairs than the profession will admit.

Here come the numbers

Note that the last entry in the above guidelines for survey retracement is “coordinates.” In accordance with most accepted lists, coordinates can be local or geodetic. These coordinate values are generated by surveyors, geodesists and public agencies; they can be found on plats, and in records and websites kept by government agencies.

Now that we are more than two decades into the 21st century, it would be safe to say that most of the surveying profession uses an established geodetic coordinate system. The use of GNSS receivers is widely accepted as normal practice by many surveyors because these systems are much more user friendly than in years past. Additional constellations have added to the availability and accuracy of GNSS positional values, so utilizing state plane coordinates has become the norm.

We are now surrounded by something that has an incredible impact on our profession and the world around us. We are placing trust in a georeferenced coordinate system that cannot be identified by any of our senses, like we can with a physical monument.

A coordinate cannot be seen, touched, tasted, heard or smelled.

We are placing our full trust in a reliable position on Earth as determined by our GNSS receiver working within a published coordinate system. Because of these advancements in technology, a new generation of geospatialists is insisting we should revise the way we survey, because technology provides much higher precision and accuracy.

Just like lines on a map or plat, coordinates only exist as a calculation of a position on the face of Earth. So why is there animosity in trusting coordinates over the more traditional items on the list of retracement guidelines? It may have to do with the fact that the ground we are surveying is not in the same place it was a short time ago. Depending on where you live, it may have moved more than you think. For more information on the shifting ground we live on, let us dig into some research about our continents.

Pangea: Description of moving land masses

(Text from USGS.gov)

From about 300-200 million years ago (late Paleozoic Era until the very late Triassic), the continent we now know as North America was continuous with Africa, South America and Europe. They all existed as a single continent called Pangea. Pangea first began to be torn apart when a three-pronged fissure grew between Africa, South America and North America. Rifting began as magma welled up through the weakness in the crust, creating a volcanic rift zone. Volcanic eruptions spewed ash and volcanic debris across the landscape as these severed continent-sized fragments of Pangea diverged. The gash between the spreading continents gradually grew to form a new ocean basin, the Atlantic. The rift zone known as the mid-Atlantic ridge continued to provide the raw volcanic materials for the expanding ocean basin.

Meanwhile, North America was slowly pushed westward away from the rift zone. The thick continental crust that made up the new east coast collapsed into a series of down-dropped fault blocks that roughly parallel today’s coastline. At first, the hot, faulted edge of the continent was high and buoyant relative to the new ocean basin. As the edge of North America moved away from the hot rift zone, it began to cool and subside beneath the new Atlantic Ocean. This once-active divergent plate boundary became the passive, trailing edge of westward moving North America. In plate tectonic terms, the Atlantic Plain is known as a classic example of a passive continental margin.

Today, the Mesozoic and Cenozoic sedimentary rock layers that lie beneath much of the coastal plain and fringing continental shelf remain nearly horizontal.

Image: USGS

In geologic terms, a plate is a large, rigid slab of solid rock. The word tectonics comes from the Greek root “to build.” Putting these two words together, we get the term plate tectonics, which refers to how the Earth’s surface is built of plates.

The theory of plate tectonics states that the Earth’s outermost layer is fragmented into a dozen or more large and small plates that are moving relative to one another as they ride atop hotter, more mobile material. Before the advent of plate tectonics, however, some people already believed that the present-day continents were the fragmented pieces of pre-existing larger landmasses (“supercontinents”).

The diagrams below show the break-up of the supercontinent Pangaea (meaning “all lands” in Greek), which figured prominently in the theory of continental drift — the forerunner to the theory of plate tectonics.

Image: USGS

Continental drift, plate tectonics and prime meridians

Historians and other scientists have theorized about Pangea for centuries. Common soil types, fossils, and other evidence found on different continents help to solidify the concept of Pangea. Items discovered on the west coast of Africa have many similarities with those found on eastern South America. The physical evidence is quite convincing that an earlier supercontinent existed millions of years ago.

Now, let’s apply a fixed measurement system with lines upon Earth that defines latitude and longitude. In the past, geodesists, geographers and mathematicians established various “prime meridians” around the world to serve as a basis for maps. Locations and cities used included Amsterdam, Antwerp, the Bering Strait, Bern, Brussels, Copenhagen, Florence, Giza, Jerusalem, Kyoto, Lisbon, Madrid, Naples, Oslo, Paris, Philadelphia, Pisa, Rio de Janeiro, Rome, Stockholm, Warsaw and Washington, D.C. (in four different places!), just to name a few.

Thankfully, scientists gathered in the 19th century to agree upon a singular “initial meridian” that would pass through Greenwich, England, and was based upon several centuries of astronomical observations at the nearby Royal Observatory.

For approximately 100 years, mapmakers (and geodesists) used the new Prime Meridian at Greenwich as the beginning baseline for longitude determination around the world. After all, it was based upon years of astronomical observations and solved the age-old problem of where longitude starts. (Latitude was a much easier calculation for astronomers and geodesists, but that story is for another day.)

Photo: majaiva/iStock/Getty Images Plus/Getty Images

The late 20th century and the fourth industrial revolution

Technology, once again, provides us with conflicting results. While most technological advancements are game-changing improvements to mankind, they also tend to shake up information and standards that have existed for many generations. Like the previously discussed advancements in telephones, technology makes us change the way we look at things and how we go about our lives.

Mapping has become a central part of our everyday lives. Georeferenced positions for literally everything is now a standard characteristic of many functions within our environment, especially in our surveying world. Most of these improvements are due to GPS, which was originally developed for the U.S. military to guide and assist with positional location of our defense systems in relation to our enemies. We use this same precise technology to establish positional locations for boundary points, infrastructure and topographic information.

Image: Tim Burch

We have also used GPS to learn much about our tectonic plates and varying movement of the continents.The first thing we learned is that the Prime Meridian established in 1884 does not fall in the same place as our 0° latitude designation as determined by GPS/GNSS calculations.

This finding, however, is not the telling item within our adaptation of GPS data; it came when various agencies established the continuously operating reference system (CORS), composed of static GPS base stations. CORS stations, while used to help establish new survey positions in relation to a known reference location, also measure a continuous drift of latitude and longitude positions over time.

The National Geodetic Survey (NGS) is in the process of finalizing a new reference framework for establishing coordinate values that utilize time as a core component. Future implementation of the new National Spatial Reference System (NSRS) will require the additional attribute of time within the metadata of any new values.

Read more in David Zilkoski’s Survey Scene column.

The reality of ‘moving’ monuments

So how does this affect surveying and the monuments we surveyors hold on such a high pedestal? The answer varies depending on who one asks. Most surveyors will continue to hold the “priority of calls” as listed above. Several practitioners, however, want to move coordinates higher up the list because of technology, and the ability to retrace a published point because of the increase in technology and the higher accuracy and precision of today’s GNSS.

This is possible if the user of the technology follows the procedures as established by NGS with metadata and accurate timing, but there are still several variables in the setting and retracing methodologies. When was the last time the equipment was calibrated? Was adequate research performed to minimize environmental errors? Was there any interference due to solar storms or multipath? There are many potential issues a surveyor can face, but few are checking all the boxes when performing highly accurate and precise positional measurements.

Technology has brought surveying into the 21st century with GPS/GNSS and ever-increasing accuracy and precision. It should also be the profession’s goal that the technology does not override what the general public can see. They can see monuments, fence lines, buildings and other improvements, but they cannot see coordinates, which remain invisible to the naked eye. Technology may change that in the future, too, but until that time, we must rely on what we can see.

<p>The post Coordinating surveyors on where we draw the lines first appeared on GPS World.</p>

Tim Burch

The board of directors of the National Society of Professional Surveyors (NSPS) has appointed Timothy W. Burch to be its new executive director. Burch took up the position on Jan. 3.

Tim Burch is a contributing editor to GPS World’s Survey Scene newsletter, authoring columns six times a year.

Burch is a professional land surveyor (PLS) licensed in Illinois and Wisconsin. He has been involved with NSPS for more than 20 years as secretary of the board of governors as well as the board of directors, NSPS vice president, a member of the Certified Survey Technician Board, Joint Government Affairs and American Land Title Association (ALTA)/NSPS Land Title Survey committees. Along with content contributor for NSPS social media, he is creator and producer of the NSPS podcast “Surveyor Says!” and a contributing writer to the NSPS newsletter “News and Views.”

Burch has been involved with the land surveying profession for more than 30 years and has represented NSPS at numerous functions and conferences. He has provided testimony on behalf of the profession at both the state and federal levels as well as helping establish a partnership with “Get Kids into Surveying.”

He is currently chair of the International Federation of Surveyors (FIG) Working Group 1.1 (Professional Ethics) and is chair-elect for FIG Commission 1 (Professional Standards).

Burch succeeded Curt Sumner, who was executive director for the past 23 years.

<p>The post GPS World contributor Tim Burch appointed executive director of NSPS first appeared on GPS World.</p>

As stated in the announcement, NGS has developed a file format for submitted real-time kinematic (RTK) data and post-processed GNSS vectors from vendor software to NGS. It is denoted as GNSS Vector Exchange Format (GVX).  This format enables NGS to incorporate the data into its GNSS processing routines.

This is similar to the original Receiver Independent Exchange Format (RINEX) developed for making post-processing more efficient when combining GNSS data from manufacturers outputting raw GPS data in varying file formats. In my opinion, this is a significant improvement to NGS’s OPUS web utility.

Beta OPUS Projects 5.0 Webpage

Image: NGS website

Users can obtain background information about the GVX file format by clicking the link GVX file format. More detailed information about the GVX format can be obtained by clicking on the Documentation link.

GNSS Vector Exchange File Format Webpage

Image: NGS website

Basically, GVX is a standardized format for exchanging GNSS vectors derived from GNSS survey data using any manufacturer hardware and software results (see the box titled “Excerpt from Documentation of GVX”).  NGS designed the format so that it included all of the necessary data (including metadata) of a GNSS vector for incorporation into a survey network for performing a least-squares adjustment.

A sample GVX file can be obtained by clicking on the link titled “Example of GVX file, project day 066, day 052, day 053, day 054.” As NGS states in the documentation, the output can be read both by humans and machines. What’s important is that it can be read by machines so the information can be incorporated into software programs. GNSS vendors have all the information they need to generate the output file to enable users to import the data into OPUS Project 5.0. Users will have to contact their software providers to determine whether their software routines generate the GVX output files.

Example of GVX file, project day 066

Image: NGS website

As I previously mentioned, this new option in OPUS Projects 5.0 is a significant improvement because many surveyors use RTK networks to obtain coordinates of marks. It will also facilitate the occupation of benchmarks with GNSS equipment to support the NGS 2022 Transformation tool. North Carolina, my home state, has a real-time network (RTN) that includes 96 GNSS CORS. (See the box titled “NC GNSS CORS and Real-Time Network.”) Currently, the North Carolina GNSS CORS and RTN has 4584 RTN service subscriptions.

NC GNSS CORS and Real-Time Network

Image: North Carolina Geodetic Survey Website

I could not find a current list of public RTK networks in the United States, but I did locate a Jan. 7, 2014, GPS World article by Eric Gakstatter that provided a list of public RTK base stations in the country. It’s not up-to-date, but it highlights that, more than seven years ago, more than half of the U.S. states  had some kind of public RTK network. I would like to update the table, so I’d appreciate receiving information on the status of any public RTK network. Please feel free to send me an email at geospatialsolutionsbydbz@gmail.com.

Why do I believe that this new option in OPUS Projects 5.0 is so important? Because it facilitates the incorporation of accurate GNSS-derived ellipsoid and orthometric heights into the National Spatial Reference System (NSRS).  With the development of improved algorithms, the results of coordinates computed using GNSS CORS/RTNs are more accurate today than ever before. During the last decade, there have been many studies analyzing GNSS data to estimate the accuracy values of coordinates from RTN data.

A study titled “Accuracy of GNSS Observations from Three Real-Time Networks in Maryland, USA” by Daniel Gillins, Jacob Heck, Galen Scott, Kevin Jordan and Ryan Hippenstiel presented at FIG Working Week 2019 in Hanoi, Vietnam, April 22–26, 2019, provided a comparative evaluation on the accuracy of three independent RTNs constructed with differing hardware and software. Their study was based on 486, 5-minute duration GPS + GLONASS network RTK (NRTK) observations. The results indicated that repeat NRTK vectors could be combined to meet 1 cm horizontally and 2 cm vertically (ellipsoid height) accuracies at 95%. confidence.  See the box below.  It should be noted that the repeat observations should be observed at different times of the day (for instance, separated by > 2–3 hours), as well as, in my opinion, if possible at least more than two different days.

Lastly, I would like to remind users that only three months remain until the December 31, 2021, cutoff to submit GPS on Benchmarks data that NGS can guarantee will be analyzed to compute the initial set of 2020.0 Reference Epoch Coordinates (RECs) that will be released with the Modernized NSRS. This initial set of RECs is currently the only set that NGS can guarantee will be used to build the 2022 Transformation Tool.  Once the transformation model is finalized, the NAVD 88 – NAPGD 2022 transformation values will be locked in and will not be updated as additional sets of RECs are computed.  If you have questions or concerns about this cut-off date, please contact your NGS Regional Geodetic Advisor, or drop NGS a line at ngs.gpsonbm@noaa.gov.

Beta OPUS Project 5.0 is a web-based tool that makes it easier to submit data to NGS.  I would encourage NSRS users to occupy as many benchmarks with GNSS equipment and submit the data to NGS before the Dec. 31 deadline.  Not only will these data help in improving the transformation model, but the marks will be included in the first computation of Reference Epoch Coordinates (RECs).  You can obtain information about Reference Epoch Coordinates in NGS’s NOAA Technical Report NOS NGS 67 publication titled “Blueprint for the Modernized NSRS, Part 3: Working in the Modernized NSRS.” A future column will address the different types of coordinates that will be distributed by NGS with the modernized NSRS.

<p>The post NGS Beta OPUS released, accepting RTK and post-processed data first appeared on GPS World.</p>