What is the current geoid model that you support?

You may have noticed that in some of our apps the Feature Properties window for the selected Feature provides two altitude values.

HAE is Height Above the Ellipsoid, or the ellipsoidal height. This is the height your GPS receiver records in reference to the ellipsoidal model of the earth. MSL is the orthometric height based on the Mean Sea Level, or the geoid. The difference between these two height values are different at different locations.

The tabulation of the separation between the ellipsoid and the geoid over a grid is what’s called a geoid model.To help compute the MSL height, the NGS in the USA provides a geoid model that is updated from time to time.

iCMTGIS PRO users who connect to a precise external GPS receiver will be able to obtain more accurate MSL height values if they place the NGS binary geoid file for the region of interest in the Documents folder for iCMTGIS PRO. We have broken the NGS geoid12a files into smaller sections and converted them into our geoid separation (*.g1) files that can be used with iCMTGIS III and iCMTGIS PRO. After transferring the .bin or .g1 files to the Documents folder of iCMTGIS III or iCMTGIS PRO, please restart the app to make it work.

If you are using iCMTGIS III or iCMTGIS PRO and would like to get our .g1 files, please email support@cmtinc.com to request them.


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