About Changing the Specified Coordinate System of a DEM File

Use the Prospector tree to specify or change a DEM file coordinate system. If the DEM file coordinate system is different from the current coordinate system of the drawing, you can specify a coordinate system for the DEM file. The coordinate system you specify for the DEM file should match the data defined in the DEM file itself.

Note: Specify a coordinate system for the DEM file only if the coordinate system of the DEM file is different from the current coordinate system of the drawing and you want a coordinate transformation to occur when you build the surface.

If you used the wrong coordinate system when adding the DEM file, you can select a different coordinate system for the file by changing the DEM file properties.

Note: If the coordinates are transformed, the points no longer lie on a grid. Therefore, the transformation of DEM data is not supported when adding a DEM file to a grid surface. You can change a DEM coordinate system only when adding a DEM file to a TIN surface.

The following table lists some specific examples about how coordinates are read and processed when using various coordinate system settings in your drawings and DEM files:

When the DEM Coordinate System (source) is set to...	And the Drawing Coordinate System (destination) is set to...	The following results occur:
NH State Plane NAD27	NH State Plane NAD83	The DEM file coordinate data is transformed from NAD27 to NAD83 when you build the surface.
NH State Plane NAD27	None	The DEM file data is not transformed when the surface is built; the DEM file data is taken at face value. For example, point 100,100,100 in the DEM file is point 100,100,100 in the surface.
None	None	The DEM file data is not transformed when the surface is built; the DEM file data is taken at face value. For example, point 100,100,100 in the DEM file is point 100,100,100 in the surface.
None	NH State Plane NAD83	The DEM file data is not transformed when the surface is built; the DEM file data is taken at face value. For example, point 100,100,100 in the DEM file is point 100,100,100 in the surface.
NH State Plane NAD83	NH State Plane NAD83	No transformation is applied. Note: Specifying a coordinate system for a DEM file is not necessary in this situation. However, if you are working with multiple drawings in the current project, and the drawings have different coordinate systems, it is recommended that you specify a coordinate system for the DEM file in case you need to rebuild the surface in a drawing that has a different coordinate system.