Tag: CORS

Last year I was privileged to be part of a Blue-Ribbon Review Panel for an American Society of Civil Engineers (ASCE) surveying publication. The book is Surveying and Geomatics Engineering: Principles, Technologies, and Applications. I recently received my copy of the published book in the mail and decided to highlight some sections. While preparing this column, the chapters reminded me of how geodesy has expanded into so many different disciplines.

I first mentioned this in my July 2020 article for the “First Fix” column of GPS World, where I stated that the shortage of American 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 and drones), navigation, precision agriculture, smart cities and location-based services. That is why I believe understanding geodesy is more critical today than ever. In January 2022, Mike Bevis, collaborating with others, prepared a white paper titled “The Geodesy Crisis,” documenting the concern about the lack of trained geodesists in the United States.

“The inverted geospatial pyramid” graphic depicts how the entire $1 trillion geospatial economy is supported and dependent on geodesy, and how it’s close to collapsing without an increase of support for 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.

In my opinion, without investment in geodesy, the United States will not have the available skills and knowledge to develop new geodetic technologies and improve models to address challenges to society, such as

• how the Earth’s surface is changing as sea level rises and the Earth’s glaciers and ice sheets change on timescales of months
• how the tectonic plates are deforming and what physical processes control earthquakes, and
• the ability to monitor the temporal changes in Earth’s water reservoirs by measuring changes in Earth’s gravitational field as it responds to the moving water mass and the deformation of the solid Earth caused by moving water.

These challenges need a well-maintained, stable terrestrial reference frame (TRF) with sub-1 mm/year vertical accuracy. Errors in TRF heights can propagate systematically into estimates of atmospheric water vapor, sea level, satellite orbits and other parameters. An accurate TRF can lead to important observations and discoveries because it enables revelations from coherent global motions. (My previous column described the latest International Reference Frame of 2020 [ITRF2020].)

Geodesy has been a significant part of my life for 50 years. I’ve seen a lot, and unless we address the Geodesy Crisis, the innovations in geodetic science of the past will not continue in the future. At least not in the United States.

The Geodesy Crisis paper was mentioned in the Fall 2022 ION Quarterly Newsletter by Everett Hinkley (see the box below). Hinkley noted, “The geospatial community relies on geodesists, though few in the community are fully aware of this connection nor understand the importance of geodesy to their work.” I encourage everyone to download the white paper and the ION Quarterly Newsletter to understand the importance of the need for more trained geodesists.

Excerpt from Everett Hinkley’s Article

“In January 2022, a white paper entitled America’s loss of capacity and international competitiveness in geodesy, the economic and military implications, and some modes of corrective action was released (Bevis et al.). This collaborative paper paints an alarming picture of the dwindling pool of trained geodesists within the United States. The report highlights America’s loss of capacity and international competitiveness in geodesy and states: ‘The U.S. is on the verge of being permanently eclipsed in geodesy and the downstream geospatial technologies. This decline in capability threatens our national security and poses major risks to an economy strongly tied to the geospatial revolution, on Earth and, eventually, in space.’ Though the word crisis correctly describes the dire predicament well, it didn’t occur overnight. Due to several converging trends, the geodesy crisis has been decades in the making. A national lack of geodetic expertise presents a significant challenge with downstream impacts on positioning, navigation, mapping, and dependent geospatial technologies. The Department of Defense, intelligence community, and federal civil agencies’ mapping entities rely on accurate and precise maps for a broad range of purposes, and reliable maps depend on an accurate geodetic underpinning. The geospatial community relies on geodesists, though few in the community are fully aware of this connection nor understand the importance of geodesy to their work.” (Reproduced with permission from ION.)

In my “First Fix” column, I mentioned that I attended The Ohio State University (OSU) to obtain my graduate degree in Geodetic Science in 1979. Therefore, I admitted that I am a little biased — once a geodesist, always a geodesist. That said, in OSU’s geodesy heyday (1960–1990s), many Americans trained were sent there by federal agencies: National Geospatial-Intelligence Agency (NGA), NOAA/National Geodetic Survey (NGS), USGS, Army, Navy and Air Force. During the 1970s, NGS sent two employees back to school every year. These agencies needed geodesists because they were undertaking significant projects, such as the NGS projects to readjust the U.S. national horizontal (NAD83) and vertical geodetic (NAVD88) networks. I was one of the employees NGS sent to OSU to be trained to support the NAD83 and NAVD88.

Today, the environment is different. U.S. federal agencies still need geodesists to develop enhanced and refined geodetic models and tools. However, major U.S. companies, such as Google and FedEx, the automobile industry, the construction industry (automated machine guidance), precision farming companies and mining companies also need more accurate geodetic models, tools and algorithms. Therefore, these companies also need trained geodesists to perform essential research on topics that address their geodetic requirements. As indicated in “the inverted geospatial pyramid” graphic, the entire $1 trillion geospatial economy is supported by geodesy.

As implied in Hinkley’s article, geodesy has played a role in developing geospatial products but most users didn’t realize that it was their foundation. Since it’s been in the background, everyone assumes it will always be there. A participant at one of my workshops stated that “GPS has made geodesists out of all of us.” In my opinion, the advancements in GNSS equipment and processing software provided some users with a “false sense of knowledge or security” that they understood what was happening within the “black box.” One of my colleagues at NGS said that the new equipment and software programs were creating a field force of “buttonologists.”

These statements concerned me at the time and concern me today. With the last generation of trained geodesists either retired or getting ready to retire, we are at a critical stage of not being able to meet the geospatial needs of the future. As indicated in the white paper, there are significant challenges in rebuilding programs that support the training of geodesists.

Hinkley’s article summarized several action items that could help improve the lack of trained geodesists in the United States. I’ve provided his list in the box below. I’ve highlighted several items the surveying and mapping community can help achieve.

So how do we build and educate the next generation of geodesists?

• Make the White House and Congress aware of this crisis, particularly its national security implications; seek direct support in the federal budget to correct this issue. It has become clear that, without engagement at the highest echelons of the U.S. government, averting this current crisis and its eventual outcome is unlikely.
• Teach rigorous math in our public schools; follow the scholastic math approach used in many Asian and European countries.
• Encourage creative thinking!
• Actively market geodesy in high schools as a rewarding career for the math stars before college entry.
• Build back, support and sponsor geodesy programs at select universities. This support needs to be strategic, with backing from the highest levels of the U.S. government.
• Break our cultural trend of reactions to crises and seize the opportunity to be proactive and prevent the foreseen consequences of this crisis.
• Encourage U.S. government support in the form of grants, professional development of staff, and research collaborations/affiliations. There are early efforts underway to bring new talent into the pipeline:
  • the National Geospatial-Intelligence Agency (NGA) is forming an emerging scientist consortium (ESCON) with partnerships that exist with Ohio State, UT-Austin, and other industry/academic/government partners
  • a pilot Ph.D. geodesy educational program with three NGA and one NGS employee is in place; the NGA expects to continue growing this program.
  • the NGA’s new western headquarters in St. Louis will bring 350 companies and organizations into the regional GEOINT ecosystem.

If we answer this call to action collectively, there is hope that a new cadre of U.S. geodesists can be cultivated before it’s too late to recover.

(Reproduced with permission from ION.)

With all that said about the need for more geodesists, one thing that this ASCE publication may do is make some readers realize how much they don’t know about the roots of the technology that they’re using to create geospatial products and services. This knowledge gap is not just correctly using GNSS and other geospatial technology to perform a survey, but also integrating various instruments to create an accurate mapping system, such as mobile mapping and terrestrial laser systems. My intent is not to criticize the expertise or knowledge of anyone, and I only mean to point out that in today’s use of computers and programs, many technical concepts are hidden in “black boxes.” I learned many things about some topics by reviewing this book.

The book is 556 pages and has 15 chapters. As part of my responsibilities as a Blue-Ribbon Panel member, I read every word in the book, and not many people will read the entire book. Still, I would encourage surveyors, engineers, geodesists, photogrammetrists and GIS and remote-sensing practitioners to obtain a copy of the book for reference and to understand the limitations of geospatial technology.

Now to the book’s content. I want to highlight that the forward is written by Juliana Blackwell, director of the National Geodetic Survey (NGS). She states that “A common thread running through the manual is the importance of the National Spatial Reference System (NSRS) to modern geospatial applications.”

Most of my columns highlight something relevant to the NSRS. That’s because the NSRS is the foundation layer for United States federal geospatial products, and geodesy provides the foundation for all geospatial products and services as indicated in the “The inverted geospatial pyramid” figure.

I would also like to highlight a statement by Gene Roe in the preface. He states, “Because entire books could be devoted to each of these topics, this manual only provides a summary, and it points the readers to important references where they can find more details. The manual is meant to provide a comprehensive but general overview to help support education and inform practicing engineers on the important role of the surveying engineer. It is too important for this not to occur.”

I agree with Roe’s statement that the book is important for surveying engineers. Still, I would add that this book is important to anyone working with GNSS and other geospatial data, especially geodesists, surveyors and GIS practitioners.

This publication is edited by three individuals that are licensed surveyors; two of them are geodesists who work for NGS. These individuals have performed a fantastic job of ensuring that all chapters have been reviewed for correctness and that the information provided is current and essential for users of geospatial data.

Readers can download copies of the book and specific chapters here. You can buy it as an e-book or in print. The “Abstract” box summarizes the book from the ASCE Library website.

Abstract

Sponsored by the Surveying Committee of the Surveying and Geomatics Division of the Utility Engineering and Surveying Institute of ASCE and the National Geodetic Survey of the US National Oceanic and Atmospheric Administration

Surveying and Geomatics Engineering: Principles, Technologies, and Applications, MOP 152, is a comprehensive yet general overview to help support education and inform practicing engineers on the important role of the surveying engineer. It provides a much-needed update on the modern practice of surveying and geomatics engineering.

Topics include:

• geodesy
• coordinate systems and transformations
• least squares adjustments and error propagation
• modern surveying and remote sensing technology
• analysis and establishment of control
• geographic and building information systems
• construction surveying, and
• best practices.

MOP 152 can be used as a summary and a reference for practicing engineers, surveying and otherwise, to help provide a solid understanding of the state of the surveying and geomatics engineering field.

Below is a list of the chapters and their authors. This column cannot highlight everything important in this book, but I will select a few items to which I believe users of geospatial data should pay attention.

Chapter Titles

As a geodesist, I usually focus on topics relevant to geodetic science. This book has a lot of topics that use geodesy concepts to create an engineering product or service. For example, chapter 2, “Geodesy and Geodetic Computation” by Earl Burkholder, provides a good summary of geodetic concepts that anyone using or generating geospatial products should know and understand. It gives basic equations without lengthy derivations of how they were developed.

In my opinion, chapter 3, “Map Projections and Local Coordinates Systems” by Michael Dennis, does the best job of explaining the concepts of map projections that are relevant to the surveying and mapping community. Many GIS practitioners use map projections in their software but don’t have a working knowledge of what’s happening to their original data. This chapter describes the current United States State Plane Coordinate System of 1983 (SPCS83) and the future State Plane Coordinate System of 2022 (SPCS2022) that is scheduled to be adopted in 2025. Dennis uses figures and diagrams to describe map projections, angular and linear distortion, and methods for reducing map projection distortion to make it easier for readers to understand the concepts. One section of interest to many surveyors after SPCS2022 is adopted is the Low-Distortion Projection (LDP) Coordinate Systems section. This is useful because, in SPCS2022, many states have designed LDP systems for their state’s SPCS2022. The box below provides a diagram with the number of zones for each state.

One purpose of an LDP is to reduce linear distortion; it is not a new concept. Many surveyors have performed a simplified form of it for decades. It’s known by many as a “modified” or “scaled” State Plane. The American Congress on Surveying and Mapping (ACSM) taught a workshop for decades describing how to compute a “modified” State Plane Coordinate. I was an instructor of this class in the 1980s and 1990s. “Modified” State Plane Coordinates had several issues, but they worked reasonably well in small areal extents. Today, with the advancements in computers and computer software, there are better ways to accomplish an LDP. Dennis’ section does a great job explaining the new SPCS2022 and the design of LDPs in the SPCS2022. The use-case examples provide a simplified description of understanding the linear distortion behavior in an area.

Chapter 4, “Local, Regional, and Global Coordinate Transformation” by Michael Dennis, is one that every surveyor and GIS practitioner should read. Dennis highlighted the differences between “equation-based” transformations and “grid-based” transformations, as well as combined equation-based transformations with grid-based transformations. Understanding the information provided in chapter 4 will be important when NGS replaces the NAD 83 (2011) and NAVD 88 datums with the new, modernized NSRS in 2025. NGS will provide models and tools for users to perform coordinate transformations, but hopefully, some users will want to understand what’s happening behind the scenes.

Chapters 8 and 9 discuss laser scanning systems. In chapter 8, “Terrestrial Laser Scanning,” the “Data Quality Considerations” section highlights common artifacts or limitations encountered with terrestrial lidar system data. The authors provide many examples of these artifacts, making the concept easy to understand. At the end of this chapter, there are 14 pages of references that will be very helpful to users involved with terrestrial laser scanning systems.

Chapter 9, “Mobile Terrestrial Laser Scanning and Mapping,” is very informative, especially the section on georeferencing. This section is not just the description of properly using GNSS to perform a survey, but also the integration of various instruments to create an accurate mobile mapping system. I like how the authors discussed the error sources in georeferencing the system, listed the source, and provided an explanation of the error.

Anyone performing a GNSS survey project that meets NGS’s requirements needs to read chapter 11. I like the section describing how users should evaluate CORSs before using them as control. Evaluating CORS is something all users should do before using any CORS in their project, because not all CORS are created equal. See the excerpt from chapter 11 below for the recommended steps from the author.

Excerpt from Chapter 11 – Steps for Evaluation of CORS

The author recommends the following steps:
1. Choose stations that are within 100-300 km of a project site. It is well known that errors in GNSS baseline processing are directly correlated with baseline length (Chapter 6). Tropospheric delay is reduced when baselines are shorter and atmospheric conditions at each end of the line are similar. In addition, mutual satellite visibility at each end of the line for differencing diminishes as baselines grow longer. That said, errors in GNSS processing are more occupation time-dependent than baseline length-dependent (Eckl et al. 2001). Therefore, for short GNSS sessions (i.e., < 2 hours), choose CORS within approximately 100 km as control; for moderate GNSS sessions (i.e., 2 to 8 h), choose CORS within approximately 300 km. Note that even longer baselines can be successfully processed when GNSS sessions are very long in duration (e.g., up to 2,000 km for 24 h sessions).

2. Determine if GNSS data are available at a given CORS during the time of your survey. Of course, if data are unavailable, then the station simply cannot be used as control. NGS provides a tool known as “User Friendly CORS (UFCORS)” for entering a date and time range to view available data at a given station (NGS 2021c). This tool can also be used to download the raw GNSS data for processing and adding a station to the survey network.

3. As discussed previously and when possible, choose a CORS with computed velocities rather than modeled velocities from HTDP. NGS provides tables of official coordinates with “computed” versus “htdp” coordinates and velocities on the website for CORS.

4. Review the aforementioned short-term time-series plot for the station, ideally at the time of the project. Stations with large spikes, data gaps, bias from the published “red” line, or large standard deviations should be avoided. A good rule-of-thumb is for the RMS in the short-term time-series plot (Figure 11-2) to be less than 1.0 cm in north and east and 2.0 cm in the up direction in a local geodetic horizon frame at the station.

5. Examine the formal uncertainties for the official coordinates of the CORS. Standard deviations in north, east, and up are provided on the station’s datasheet, accessible from the webpage for the CORS (more on datasheets are discussed in the following under Passive Control). Stations with unusually large standard deviations (> 3 cm) should be avoided. Note that standard deviations are not available for CORSs with modeled velocities.

I believe that the evaluation of NOAA CORS is critical, so I’ve described Dan Gillins’ “Steps for Evaluation of CORS” below. First, users can access the NOAA CORS using the NGS CORS Map utility. After the map appears, users can move the cursor over the center of the project area, where it provides the location of the cursor and the three closest CORS. Users can click on a CORS icon and get coordinates and other information about the CORS. Also, they can place an X on the map, and the utility will draw a 250-km circle around the point. The box in the lower left-hand side of the map provides a list of the sites within 250 km of the marked location.

Using CORS Map to Identify CORS

Users can download the NOAA CORS coordinates and velocities (computed and modeled). I downloaded the files and plotted three circles (with radii of 100, 200, and 300 km) around CORS NC77 in Charlotte, North Carolina. I only plotted CORS that are operational and have computed velocities. North Carolina has a lot of CORS to select from. In contrast, I’ve plotted three circles (also with radii of 100, 200 and 300 km) around CORS WYRF in Casper, Wyoming.

Buffer Zones around Charlotte, NC

The plot depicting the buffer zones around Casper indicates that there are no CORS within the 100-km circle and only a few between 100 and 200 km.

Buffer Zones around Casper

The data availability of the CORS site can be obtained by clicking on the CORS icon, selecting “Get Site Information,” and then selecting “Data Availability.”

Data Availability at CORS NC77

The position and velocity for the CORS can be obtained by clicking on the Coordinates button on that CORS webpage.

Position and Velocity Sheet for CORS NC77

The CORS Short- and Long-Term plots can be obtained by clicking on the Time Series button on that CORS webpage.

Short-Term Plot of CORS NC77

The Datasheet for the CORS can be obtained by clicking on the Coordinates button and then on the Datasheet button on that CORS webpage.

Datasheet for CORS NC77

There are too many chapters to describe each one, but I encourage users to check each chapter’s abstract on the ASCE website and decide which ones would be the most beneficial to them (see the box titled “Abstract for Chapter 11 Survey Control”). The manual provides numerous references and can serve as a helpful resource for finding further details on the fields of geodesy and surveying.

Abstract for Chapter 11 Survey Control

A goal of mine is for some readers of this column to obtain enough knowledge to “whet their appetite” and encourage them to pursue an education in geodesy and surveying. Others who are influential in federal government programs and those responsible for geospatial research for industries will recognize the need for more trained geodesists in the United States and help by doing the following:

• actively market geodesy in high schools as a rewarding career for the math stars before college entry
• build back, support, and sponsor geodesy programs at select universities; this support needs to be strategic with backing from the highest levels of the U.S. government
• encourage U.S. government support in the form of grants, professional development of staff, and research collaborations/affiliations.