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I'm trying to create a CRS for a local mine grid that involves the translation and rotation of GDA94 / MGA zone 55. The origin is translated 2195129.073 in the +x direction and by 5489615.789 in the +y direction, then the x-y plane is rotated about the origin by 68303 arc seconds. This is the proj4 for GDA94 / MGA zone 55:

+proj=utm +zone=55 +south +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs

This is the proj4 I have used to try and make the local mine CRS:

+proj=utm +zone=55 +south +ellps=GRS80 +towgs84=2195129.073,5489615.789,0,68303,68303,0,0,0 +units=m +no_defs

The custom CRS currently doesn't work.

Why is it not working?

Test points; Custom Grid (15360, 6840), GDA94/MGA55 (303370.3,5916524)

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    The towgs84 parameter uses a 3/7 parameter transformation that works in XYZ (3D Cartesian space. You've got 2D conformal parameters. Look at proj v5 to see if it supports a conformal or affine transformation. Make sure you set the parameters correctly--if converting to the mine grid, the translations would be negative, for instance. – mkennedy Nov 3 '18 at 17:37

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