University of Wisconsin–Madison

Wisconsin Geospatial News

Clarification on new NGS geoid model

I received the following information from John Ellingson, Wisconsin’s State Geodetic Advisor for the National Geodetic Survey (NGS).  It seems a new geoid model released by NGS is causing some confusion in the surveying community:

“On April 23, NGS released a new geoid model that is a revised version of GEIOD12A. The new model is known as GEOID12B. I received an email this morning from one of the county surveyors asking me if you should now be using the new version, GEOID12B. My advice is that it is not necessary for you to change your GPS equipment/software to reflect the new model. Read on for details.

The NGS GEOID Team has informed us that the new model is EXACTLY the same as the earlier GEOID12A model in the fifty states (CONUS). The only change with the new version is that they have updated the portion (of the earlier geoid model) that covers Puerto Rico and the US Virgin Islands. So, unless you are surveying in Puerto Rico or the Virgin Islands, there is no need to make changes to your geoid model at this time.

An important point to remember…. You should only be using the GEOID12* model if you are working with NAD 83(2011) ellipsoid heights. If you are working with ellipsoid heights determined via earlier adjustments of NAD 83, I suggest that you use GEOID03. If you have any questions about what geoid model to use, please contact me at (202) 306-6904 or via e-mail. We can also discuss this at the Wisconsin County Surveyors Association meeting that is taking place on May 8th in Neillsville, if anyone is interested.”