English

How To: Use the Projection Utility to perform a datum shift from WGS84 to NTF

Procedure

I have data in WGS84 that I want to shift to NTF. If in step two or three of the Projection Utility I set the Geographic Transformation to WGS84_to_NTF my results are incorrect

Answer:

The Geographic Transformation option WGS_1984_to_NTF is actually performing the opposite transformation from NTF to WGS84.

Shifting from WGS84 to NTF can be accomplished by running the Projection Engine (the engine behind the Projection Utility) from the Command Prompt. In order to get the shift to work in the expected direction you must specify an Input Geographic Transformation of NAD_83_to_WGS_84_1[8088] and and Output Geographic Transformation of WGS_1984_to_NTF[8093]. The input transformation from NAD83 to WGS84 is a "null" shift since all the parameters for it are zeros. The purpose for doing this is that it will cause the output transformation of WGS84 to NTF to work in the expected direction. This double transformation (also known as a "pass-through transformation, since we are going from one datum to another via an intermediate datum) cannot be accomplished in the Projection Utility because it will not allow you to specify an Input Geographic Transformation when your geographic coordinate system is WGS84.

Example:

>projutil.exe -q -if c:\data\wgs84.shp -ic 4326 -oc 4275 -ig 8088 -og 8093
-of
c:\data\ntf.shp

Explanation of these parameters

-q to run the utility in Quiet Mode
-if the input shapefile
-ic the input coordinate system, GCS_WGS_1984[4326]
-oc the output coordinate system, GCS_NTF[4275]
-ig the input geotransformation (or datum shift), NAD_83_to_WGS_84_1[8088]
-og the output geotransformation, WGS_1984_to_NTF[8093]
-of the output shapefile