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How to convert GPS points in WGS84 to local Still Water Mine Grid?

I got GPS points in WGS84, and just have info: Datum Still Water 0.0 to NAD_27_Montana South: 1903090, 506795 , rotation = -19.9988.

Any ideas about this?

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You have two conversions to do. The first is to get the WGS84 coordinates converted to NAD27 State Plane Montana South. That includes converting between WGS84 and NAD27. Depending on data accuracy, you could try using NAD_1927_To_WGS_1984_79_CONUS which uses the NADCON CONUS grid file. Technically that file converts between NAD27 and NAD83, but again, it'll depend on the data accuracy.

The next step is to try to convert the State Plane coordinates into the Still Water Mine Grid. In ArcGIS Desktop, it's possible to set translation/rotation/scale values for a CAD layer. I would suggest convert your data into a CAD layer and trying this to see if the information you've been given works.

You have translation and rotation values. To convert from NAD27 State Plane, you'll need to use the negative translation values: x = 1903090, y = 506795. The rotation is probably also opposite so, +19.9988.

See Defining a coordinate transformation topic in the help system.

Disclosure: Esri employee

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