On Apr 24, 7:13 am, "[email protected]" <[email protected]>
wrote:
> Is the some place that has the formulas that these SPC x/y systems are
> based on?

there's the classic book "Map Projections, A Working Manual" by USGS,
which is a 20megabyte pdf available at:

http://pubs.er.usgs.gov/djvu/PP/PP_1395.pdf

page 52 has the table which defines which projection is used for each
State Plane.

The formulas are based on the earth as an ellipsoid, not a sphere, so
there's no closed-form formula for reverse transformation (from
projection to latlng).  This requires iteration using taylor series to
convert the coordinates.  Not a simple task!

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