These GPSonBM Updates have generated a lot of excellent comments and discussion, so we’ve expanded the introduction this month to add some additional information about heights, geoids, and why GPSonBMs is vital to transitioning to the Modernized NSRS:

GPS on Bench Marks is your ticket to the new positioning paradigm of the Modernized National Spatial Reference System. GPS on Bench Marks will continue even after the looming cutoff date for data inclusion in the NAVD 88 - NAPGD2022 Transformation Tool. Crowdsourcing and submitting geospatial data to NGS is how the Modernized NSRS will be realized and accessed. 

Heights in the Modernized NSRS: The NAPGD2022 heights will be determined by using GPS/GNSS observations to obtain ITRF20 ellipsoid heights and applying the corresponding geoid values from GEOID2022, the purely gravimetric geoid model that will be created using GRAV-D and other data. NGS has been producing a series of experimental geoids, called the xGEOIDs, iterating over the past seven years ever closer to what GEOID2022 will be by adding new data collected over the previous year and applying advances in modeling theory and other research findings. 

Geoid Models in the Modernized NSRS: There is a fundamental difference between the purely gravimetric xGEOIDs and the series of hybrid geoid models that NGS has produced over the past 20+ years to compute GPS-derived NAVD88 heights (GEOID96 to the current model GEOID18). The primary difference is that GPS on Bench Marks data was used in the hybrid models to constrain/warp a gravimetric geoid model (xGEOID19) to published NAVD 88 heights. While this process enabled GPS users to obtain NAVD88 heights, it also introduced additional error into the overall results. To avoid further error from warping to the NAVD88 surface, the GPSonBM data will NOT be used in defining GEOID2022.

In the Modernized NSRS, GPSonBM data WILL be used to generate Reference Epoch Coordinates (REC), create Survey Epoch Coordinates for time-dependent positioning, and create transformation grids. Data submitted after the 2020.0 REC cut-off date will be used to create the 2025.0 RECs. The GPSonBM priority lists and goals will evolve, but your data contributions will always be used to improve the NSRS in the places you use it most. The bottom line is that GPSonBM is here to stay and your participation now will prepare you to start deriving the benefits of the Modernized NSRS immediately upon its release.

Transformation Tool Campaign Countdown

Four months now remain until the December 31st, 2021, cutoff to submit GPS data that NGS can guarantee will be analyzed to compute the initial set of 2020.0 Reference Epoch Coordinates (RECs) to 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. Additional sets of RECs will be computed regularly as new data are submitted.   Once the transformation grids are created and approved, the NAVD 88 - NAPGD2022 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 Regional Geodetic Advisor, or drop us a line at ngs.gpsonbm@noaa.gov.

Recent Progress

Data submissions have remained strong this summer, with the last three months being in the top 5 months ever and June taking over the top spot. While participation still varies greatly from state to state, we are starting to see some increased interest and enthusiasm (and even some concern) from some states with big remaining data gaps. Here’s a shout-out to partners in Texas and California who are rallying the troops and working to increase participation. There are many examples around the country of individuals who are having outsized impacts on their state’s or region’s data coverage. Thank you, and keep up the good work!

Tool Highlight: New Features Added to Web Map

In response to feedback we’ve received from partners across the country, the GPSonBM Transformation Tool Campaign Web Map Application now allows users to plot the Secondary Marks along with the primary mark identified for each 10 km hexagon on the map. This improves users’ ability to conduct “desktop reconnaissance” and access datasheets for other marks that will meet the requirements for a mark’s use in creating the NAVD 88 to NAPGD2022 transformation grids.     Users will see the new “Secondary Marks” layer in the Layer List, but due to bandwidth limitations will only be able to select and display them once the map is zoomed in to city level. The Priority List of Marks shown on the map are selected automatically based on the metadata that NGS has for each mark, however, new data on any of the secondary marks will also meet NGS goals for data coverage. We encourage you to use your local knowledge and professional judgment to decide which marks on the map would be the best to observe in your area.

Call to Action: Listen, Observe & Submit

Review the map to find priority marks in your area. Watch a short video on how to Share your OPUS Solutions. Get the big-picture overview from the GPSonBM Update from 2021 Geospatial Summit  Listen to the June 10th edition of the NGS webinar series  to learn more about how geoids fit into the GPSonBM puzzle from Dr. Kevin Ahlgren, NGS geoid modeler and the GPSonBM “Wizard behind the curtain.”

NGS tracks participation in this campaign, but we rely on partner participation to be successful. If you have an accomplishment you want to highlight, email NGS.GPSonBM@noaa.gov.

NOAA's National Geodetic Survey 

geodesy.noaa.gov