Convert Ground to Grid Data in GIS

[ChrisHart1]

I am trying to develop a workflow to convert data that I have in ground NAD83 UTM Zone 12N, conversion factor 0.999855, to UTM NAD 83 Zone 12N Grid.  Whenever I use the regular projection tools, it does not move the data. I have to always manually move it by reference points.  What is the best way to approach this?  Thanks!

[MelitaKennedy · Accepted solution]

Try defining a custom projected coordinate system for the 'ground' data. If the ground UTM coordinates are supposed to be multipled by 0.999855 to convert them to regular, grid UTM coordinates, modify the PCS parameters like this:

false easting: 500000.0 / 0.999855 = 500072.5105

false northing: Zero so keep set to zero

scale factor: 0.9996 / 0.999855 = 0.99974496302

All other parameters remain the same. If you right-click the NAD83 UTM Zone 12N in the coordinate system picker, you should be able to choose Copy and Modify. In the new window, 

Change the PCS name. 

Modify the 2 projection parameters.

Save as a .prj file.

Use the Define Projection Tool or ArcCatalog to assign this definition to your ground data.

Melita

[ChrisHart1]

This is perfect! Thanks so much!

[ChrisHart1]

One other thing, when I try to convert data in regular (grid) UTM NAD83 Zone 12N Grid data back into our ground format, it does not work. For example, I tried multiplying the false northing (500000) and scale factor by 0.999855 but the data does not line up with our existing ground data?

[MelitaKennedy]

Are you using the Project Tool and setting the output coordinate system to ground system?

Melita