# Creating Proj4 string for local coordinates

I am fairly new to coordinate system conversion, so am rather lost on the following problem.

We have been using Proj4 to convert between various coordinate systems which is fine for known coordinate systems such as MGA94 and WGS84 as the Proj4 strings are already defined.

The problem we're having is that we have some maps in local coordinates that we need to convert to a known coordinate system.

What we have

• 4 control points (X, Y, and Z) in Local coordinate system
• 4 control points (X, Y, and Z) in MGA94 (zone 51)
• 4 control points (X, Y, and Z) in WGS84

Each of the 4 control points for each coordinate system are the same 4 points on a map, just in the respective coordinate systems.

Is it possible using the known points of a defined coordinates system (such as WGS84 or MGA94 (Zone 51) to determine what the Proj4 string would be that represents the Local coordinate system to enable us to convert between them?

• Means local coordinates, some plain 2D point positions, or is there a distortion? – huckfinn Nov 4 '17 at 9:11
• Proj4 has an affine definition which can by rotating and scaling perform a conversion from local to zone 51 meters, is this what you are looking for? proj4.org/operations/transformations/affine.html – Hans Erren May 12 at 19:56