To configure county coordinate systems in either TerraScan or TerraPhoto, ascertain the proper metric projection values for the desired county system. In the GeoCue workflow management software, these can be found on the Coordinate System Picker dialog or in the GeoCue Common Folder. In LP360 or True View EVO, they are found in the Coordinate System Utility. Or, locate the published values for county coordinate systems from the various state and county surveyor websites.
The CueTip – Coordinate Reprojections, Datum Transformations and Geoid Adjustments in TerraScan covers the basics of where and how to setup coordinate systems in TerraScan and TerraPhoto.
The default ellipsoid values in the Terrasolid software are based on WGS84 and so are the values defining the GRS80 ellipsoid.
Semi-major Axis: 6378137.00000 Inverse flattening: 298.257223563000
Some county systems use a modified ellipsoid, such as our Polk County, MN example in Figure 1.
Semi-major Axis: 6378445.763 Inverse flattening: 298.2572221008827
Datum Shift from WGS84
TerraScan always assumes geographic coordinates are in WGS84. If that is the case with your input data then you may need to add datum shift values to go from WGS84 to the datum on which the county coordinate system is based. NAD83(2011) is effectively equivalent to NAD83(CORS96), which is effectively equivalent to NAD83_HARN for mapping purposes and there are no defined transformations between them. The epoch date for NAD83(2011) is 2010.0 and the datum shift values are provided in the linked CueTip. If the input values are already in the NAD83_HARN of our example then we can leave these values as zero so no datum transformation will be applied.
Note: If the user does not have access to GeoCue, another location to ascertain this info is using NOAA’s HTDP utility.
Select the applicable projection type and then enter the values for the projection. Select the desired units for the data.
Important Note: All linear values in the TerraScan and TerraPhoto Projection System dialog must always be in meters. TerraScan first applies the unit conversion to the data before any projection and/or datum transformation parameters.