Custom Geoid

Custom Geoids may be created from elevation grid data in the Global Mapper application. The grid is exported from Global Mapper to the Elevation Grid Format 'Blue Marble Gridded Data' (.bgd). The BGD file may then be imported for use into GeoCalc by creating a new vertical transformation for the custom Geoid. Using a custom geoid in GeoCalc will require access to Global Mapper v16 or later.

To procure the BGD file from the Global Mapper application, load the elevation grid data into Global Mapper. Then, to export the data from Global Mapper, go to File > Export Elevation Grid Format... and in the 'Select Export Format menu, select 'Blue Marble Gridded Data' from the drop down menu.

The Blue Marble Gridded Data Export Options dialog will populate, where you may name the quadrangle, define the vertical units and select a resampling method, elect to generate a PRJ or interpolate to fill gaps.

Once the elevation grid/custom geoid has been exported BGD file and added to GeoCalc as a new, custom vertical transformation, this will be available when selecting a Coordinate Transformation.