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I am currently building a GIS database, and the engineers involved in the project have requested that we use their Modified State Plane Projection. Here are the details:
*Based off of Colorado Central Zone (0502), NAD83 (ft)
*Project Combined factor = 0.999706760
*Reciprocal = 1.000293326
*Coordinates are truncated by subtracting the following:
-1,000,000 from Modified SP Northing values
-2,000,000 from Modified SP Easting values
It can be summed up as:
Custom Northing = SP Northing x 1.000263326 - 1,000,000
Custom Easting = SP Easting x 1.000263326 - 2,000,000
This seems like it should be pretty straight-forward, but I have been banging my head against ArcGIS trying to get the new data to line up against data in an unmodified projection. I can get points to project properly against other data by applying the inverse of the formula on the shape field in the field calculator, but I need to apply the modifications as a projection file (ie I don't want to actually reproject any data)!
I have not had success defining this new projection as a .prj. I have posted my best attempt at it below. I have simply subtracted 1,000,000 from the false northing and 2,000,000 from the false easting, and applied a scale_factor of 1.000293326, but the data is not lining up correctly.
What I THINK is going on is that ArcMap may be applying the false northing/easting first, and THEN the scale factor. It needs to be the other way around: scale factor first, and then coordinate truncation. I think that's why the field calculator is working, because I can control the order of the modification. I'm grasping at straws here...
Does anyone has any ideas on what I can do to properly define this projection? Thanks for any help or comments. |