What projection does Opnet use when it displays a GeoTiff map and DTED/DEM data? I have noticed a discrepancy of as much as 500m when I load in a Geotiff map. I have tried using maps in the LAT/LON and UTM projections at a scale of1:100,000, in both the NAD27 and WGS84 datums. The discrepancy occurs in both maps.