Baythymetry river/lake elevation
I am trying to create an elevation grid from Baythymetry(water depth for a lake) information that has elevation data in feet. Global Mapper creates the grid but changes the elevation so that the grid is much higher than the elevations provided from the Baythymetry data. How do I keep the same elevation? In the Elevation Grid Creation Options, I choose feet. The depth of the lake ranges from about 500' to 680' above sea level. After the grid is produced the elevation grid is about twice as big (1000' to 1500'). I'm not sure what I am doing wrong. Pleas help.