Tag: NGS GPS on Bench Marks

New feature in OPUS Projects: Using RTN vectors to support 2022 Transformation tool

February’s column focused on potential errors in orthometric heights using a digital barcode leveling system with multi-piece leveling rods. As stated in the column, businesses need to make decisions based on expenses and ultimately on the profit margin; but making a business decision that results in a bad technical outcome is never the right decision. This newsletter column is going to highlight a new feature in the National Geodetic Survey (NGS) Beta OPUS Projects 5.1 routine permitting the use of RTN vectors to support the development of the 2022 Transformation model.

On Jan. 12, NGS held a webinar titled “Using RTN Data in OPUS Projects 5 for GPSonBM.” Users can download the video and PowerPoint slides here.

I’ve been highlighting NGS’s GPS on Bench Mark program that supports the 2022 Transformation Tool in my columns since 2018. NGS delayed the completion date for the new modernized NSRS until 2025, so they have extended the cut-off date for submitting GPS on Bench Mark data for use in the 2022 Transformation Tool until Sept. 30.

NGS GPS on BenchMarks Program (Image: NGS website)

NGS has been developing tools that facilitate submitting data to the NGS GPS on BM campaign such as OPUS Share. The latest tool is the OPUS Project 5.1 routine that allows the use of RTN vectors. OPUS Projects 5.1 is a beta product, but NGS is now allowing users to use the routine to submit data for the GPS on BM campaign. My October 2021 column highlighted NGS’s Beta OPUS Projects 5.1.

The 2023 requirements for using OPUS Projects in the GPS on BM program (Image: NGS website)

I’d like to note that OPUS has been updated to support the newly released ITRF2020 (IGS20) orbits. My October 2022column discussed the latest International Terrestrial Reference Frame of 2020 (ITRF2020) released by the International Earth Rotation and Reference System Service (IERS). A previous NGS news bulletin provided a statement about the new reference system and products.

Excerpt from NGS News Bulletin (Image: NGS website)

Clicking on the link titled “NEW: 2023 Requirements for Use in the GPSonBM Campaign” on the OPUS Projects 5.1 webpage provides the requirements for using OPUS Projects 5.1 and Real-Time Network (RTN) data to support the 2022 Transformation Tool; that is the 2023 GPS on BM campaign. There are five sections in the writeup: Introduction, Project Planning, Equipment and Configuration, Field Requirements and Office Requirements. The Introduction section states that the requirements are limited to the GPS on BM Campaign and will be replaced, or superseded, when NGS finishes its new GNSS surveying specifications.

Introduction Section from Requirement Write Up (Image: NGS website)

The project planning section of the announcement states that RTN vectors of 5-minute occupations can be used instead of the 4-hour occupations required for OPUS Share.

Project Planning Section from Requirement Write Up (Image: NGS website)

However, the Field Requirement section states that the mark must be occupied three different times.

“During the RTN survey, measure each mark in your project (including the RTN Validation Station) for a minimum of 5 minutes for three independent occupations. All three measurements must agree by 3 cm horizontal and 5 cm ellipsoid height. They also must be separated by at least 3 hours (even if occupied on different days). Plan to occupy a mark, go occupy a few more in the area, then circle back. Or rotate day-by-day,” the section states.

Field requirements Section from Requirement Write Up (Image: NGS website)

As stated in the section on office requirements for using OPUS-Projects 5 in the 2023 GPS on BM Campaign writeup,“The OPUS-Projects User Guide provides instructions on how to run the software and submit a project to NGS. The User Guide states to follow the steps in the order listed below, and it explains steps 1 – 7 and 9 – 11 in detail. For step 8 and when including GVX data in OPUS-Projects 5, refer to those portions of the User Guide’s Quick Start which are highlighted in yellow. NGS is working on fully updating the User Guide to include more details; for now, use the Quick Start Guide for assistance with GVX.”

OPUS Projects User Guide (Image: NGS website)

Quick start guide. (Image: NGS website)

I recently used OPUS Projects to analyze some GNSS results using Harris-Galveston Subsidence District CORS and PAMS GNSS data. I want to emphasize that it may seem like a lot of work the first time you use the routine, but NGS makes it fairly simple to complete each task. The manual is very complete and does a good job of describing every step. The manual can be downloaded here. In my experience, the most time-consuming task is creating the descriptions. There are several items that must be correctly entered because the answer to some entries affect the answers to other entries. That said, NGS supports a description entry software called WinDesc that facilitates entering the appropriate information. The OPUS Projects User Guide provides an appendix that describes using the WinDesc module to enter description metadata.

For marks that are in the NGS database, known as the NGS Integrated Data Base (NGSIDB), WinDesc will import information from NGSIDB, thereby decreasing the number of entries users need to address. In other words, if the mark has a PID then it should be in the NGSIDB. If you are occupying a mark that is part of NGS GPS on Bench Marks website then it probably has a PID and a description in NGSIDB.

Example of PID from Mark Priority List (Image: NGS website)

I’ve included three slides from the Jan. 12 webinar that summarize the basic requirements.

This slide is a depiction of how a CORS station must be connected to the RTN vectors. (Image: NGS website)

This slide provides the occupation and precision requirements. (Image: NGS website)

This slide provides a list of the required metadata for the project. (Image: NGS website)

As for the requirement of at least three independent RTN occupations on different times, in my opinion at least one occupation should be on a different day. My October 2021 column addressed a study that reported on using RTN solutions to estimate accurate horizontal and vertical coordinates.

The report stated, “When differenced with coordinates from a static GNSS survey campaign, the horizontal and vertical RMSE of the NRTK-derived coordinates was 2.3 cm horizontally and 4.5 cm vertically at 95% confidence. Repetitive NRTK vectors on each baseline differed between ± 2.4 cm horizontally and ± 3.4 cm vertically at 95% confidence.”

The report also stated, “Adjustment of hybrid survey networks with four repeat NRTK vectors per bench mark produced network accuracies at 95% confidence for the adjusted coordinates at all bench marks less than 1 cm horizontally and 2 cm vertically (ellipsoid height).”

The requirements are limited to the GPS on BM Campaign and will be replaced, or superseded, when NGS finishes its new GNSS surveying specifications.

(Image: Screenshot of Accuracy of GNSS Observation from Tree Real-Time Networks in Maryland, USA)

The paper by Gillins, et. al was presented at the 2019 FIG Working Week held in Hanoi, Vietnam, on April 22–26, 2019. The International Federation of Surveyors (FIG), involves a wide range of professional fields within the international surveying community; this includes surveying, cadastre, valuation, mapping, geodesy, hydrography, and geospatial and provides an international forum for discussion and development to promote professional practice and standards. FIG meetings are held all over the world. I’d like to highlight that the 2023 FIG Working Week is going to be held in Orlando, Florida, on May 28 – June 1, 2023.

NGS will be presenting a full-day worth of content on NSRS Modernization during the FIG Working Week 2023. For the first time in more than 20 years, this annual FIG gathering will take place in the United States, hosted by the National Society of Professional Surveyors (NSPS).

I’ve participated in several FIG meetings. I’ve learned a lot from presentations as well as holding hallway meetings with experts from the international surveying and mapping community. All geospatial users should plan on attending this event. I have provided information about the FIG commissions in my August 2021 newsletter. I would encourage everyone to visit the FIG website and review the information about the 2023 FIG Working Week. The a list of the FIG Commissions can be found here. More information can be obtained on each commission by clicking on its title.

Future columns will highlight the FIG Working Week as the agenda is developed. I would encourage everyone to check NGS’s Website for updates on Beta products and new surveying specifications. Geospatial users should also subscribe to NGS’s News Services at the following here. Check out the NGS News Services site for what’s available.

March 1, 2023

ArcGIS web app incorporates datasets, NGS data layers for surveyors

My last column described a new National Geodetic Survey (NGS) webtool for obtaining geodetic information about a passive mark in their database. The column highlighted some features that may be of interest to GNSS users. It provides all of the information about a station in a more user-friendly format. This column highlights an ArcGIS web application that incorporates various California specific datasets and NGS data layers to assist surveyors planning vertical control surveys. The GNSS Leveling Web Application was provided to me by Jay Satalich, chief, Office of Surveys, Caltrans (see box titled “Linkedin Notification from Jay Satalich).

Linkedin Notification from Jay Satalich

Supervising Transportation Survey (Chief, Office of Surveys) at State of California, Department of Transportation:

“GNSS Leveling Web Application” [is] an Esri ArcGIS online web app created for my “GNSS Leveling” students at College of the Canyons. Designed as a practical tool when planning vertical control surveys using GNSS. National datasets include: National Spatial Reference System (layers: satellite visibility, stability, and vertical control source), geology, and GEOID18 (layers: GEOID18 height, difference between GEOID18 and GEOID12B, and GEOID18 uncertainty). California-specific datasets include: oil/gas/fracking/injection wells, fault lines, oil fields, groundwater basins, and landslide areas. The NOAA National Geodetic Survey data layers were created and published by Brian Shaw. People who influenced development of this app include Dave Zilkoski, Kevin M Kelly, Ken Hudnut, David D Jackson, Ross S. Stein, and Arthur Sylvester.

Go to the app here.

The box titled “GNSS Leveling Web Application” depicts a map of the Los Angeles area that provides the list of published marks in NGS’ database with an overlay of the uncertainty of NGS’ hybrid geoid model GEOID18. Plotting the published marks from NGS’ database is very useful for surveyors reconning marks for a GNSS survey project. The attributes allow users to quickly identify stations that have published heights from leveling adjustments projects (labeled as ADJUSTED) and those that have heights published from GNSS adjustments projects (labeled as GPS OBS). (See here for definition of attributes.)

GNSS Leveling Web Application

(https://www.arcgis.com/apps)

The list all of the layers of the web application are provided in the box titled “GNSS Leveling Web Application Layers.” (Note: After you open up the web application, click on the Layers icon to obtain the list of available layers.)

GNSS Leveling Web Application Layers

As you can see from the list of layers, the web application enables users to select the layers that are pertinent to their survey project requirements. The application is designed for California surveyors but the concept is transferable to other States. For example, the following layers are not just for California surveyors: Arizona water wells, Louisiana oil and gas well, U.S. oil and natural gas wells, Principal Aquifers of the United States, and, of course, all of the NOAA NGS data layers.

One layer that is very important to California users is the layer that provides the fault activity in their region. The box titled “Fault Activity Map of California: Pre-Quaternary and Quaternary Faults – Quaternary Faults” depicts the list of published marks in NGS’ database with an overlay of the fault activity map.

Fault Activity Map of California: Pre-Quaternary and Quaternary Faults — Quaternary Faults

Another great feature of the application is that it has a layer providing the satellite visibility code for published NSRS marks (see the box titled “Published NSRS Stations (by satellite visibility”). Once again, a great feature for field personnel performing reconnaissance.

Published NSRS Stations (by satellite visibility)

The application also has a feature that lists the marks that were involved in the development of NGS’ hybrid geoid model GEOID18. (see the box titled “GNSS Leveling Web Application GEOID18 GPS on Bench Mark Layer”). Clicking on a mark’s icon provides information and statistics about the mark (see boxes titled “GEOID18 GPS on Bench Mark Layer — PID EW6989” and “Information for GPS on Bench Mark for PID EW6989”). This is one of the layers that provides information for the entire CONUS region. All this information is available from NGS’ website but this application incorporates all of NGS’s data as well as the local information in one application. This web application is very useful to a surveyor planning a survey project and/or providing information to a field reconnaissance team.

GNSS Leveling Web Application GEOID18 GPS on Bench Mark Layer

GEOID18 GPS on Bench Mark Layer — PID EW6989

Information for GPS on Bench Mark for PID EW6989

Users that are participating in NGS’ GPS on Bench Mark program can click on the layer for “NGS GPS on Bench Marks Transformation Service Tool, priority 10 km hex” to determine marks that need to be occupied by GNSS to improve a transformation tool being developed by NGS. See boxes titled “NGS GPS on Bench Marks Transformation Service Tool, priority 10 km hex” and “Information for GPS on Bench Mark Priority List for PID EW6989.” There’s also layers that depict the priority mark list for the GPS on Bench Marks program (“NGS GPS on Bench Marks Transformation Tool Service — priority mark list”) and the 2 km hexagon priority grid (“NGS GPS on Bench Marks Transformation Tool Service — priority 2km hex”).

NGS GPS on Bench Marks Transformation Service Tool, priority 10 km hex

Information for GPS on Bench Mark Priority List for PID EW6989

Individuals interested in participating in NGS’ GPS on Bench Mark program should register for NGS’ Dec. 10 webinar, which will discuss the status of the program. See the box titled “GPSonBM Transformation Tool Campaign Update — 12 months remaining” for the information on the webinar. Users can register for the webinar here. I would encourage all users to access the web application tool developed by Jay and/or NGS’ website before participating in the next NGS GPS on Bench Mark webinar.

GPSonBM Transformation Tool Campaign Update — 12 months remaining

(NGS webinar series)

Almost all of my columns have focused on establishing accurate GNSS heights. Most of my 45 years of working in the field of geodesy has been focused on heights; that is, leveling-derived orthometric heights, GNSS-derived orthometric heights, and geoid heights. Gravity is very important to estimating all of these types of heights. Recently, a colleague sent me a video proving Galileo’s famous gravity experiment. It’s an older video (November 2014), but it’s really fascinating. You can see the entire video here. Another individual pointed me toward the same experiment performed on the Moon during the Apollo 15 mission. What’s amazing to me is that over 400 years ago an individual spent time studying the effects of gravity and developing the concept of acceleration due to gravity. I wonder what the world would look like today if Galileo would have just accepted Aristotle’s theory of gravity (which states that objects fall at speed proportional to their mass) and decided to focus on other tasks. Saying that, I am amazed that most geospatial users do not realize the importance of gravity (and physical geodesy) in the development of the geospatial products and services that they use daily; and, how critical it is that more research is required to meet future geospatial needs. The advancements in satellites and computers have enabled geodesy to expand into many different disciplines. Geodetic science and technology now underpin many sciences, large areas of engineering (such as driverless vehicles and drones), navigation, precision agriculture, smart cities, cellular telephones, and location-based services. (See the GPS World First Fix column about the shortage of American geodesists).

When I end one of my presentations, I always emphasize that Geodesy Provides the Foundation for all Geospatial Products and Services, and Integrated and Collaborative Organizations Create Geospatial Solutions. Geodesy is just as important today as it was 400 years ago.

I hope everyone stays safe during this COVID-19 pandemic and enjoys the holidays.

December 2, 2020