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I have six control points in a local mine grid which I want to use to define a custom projection in QGIS. The reference points are in GDA94 / MGA zone 50 (EPSG:28350) (https://spatialreference.org/ref/epsg/gda94-mga-zone-50/)

Is there a way to do this in QGIS?

For clarity I want to define a CRS in the options below. Custom Projection System Definition QGIS

Bonus points if someone can explain how to define Proj4 or WKT from custom points this would be even more useful.


Points below, Reference points is MGA 94 Zone 50:

Mine X | Mine Y| MGA 94(50) X| MGA 94(50) Y
2453.122|3210.002|563053.406|7431461.771
-1735.225|-853.24|557798.872|7428929.256
5663.648|7386.58|567416.171|7434410.368
12607.859|-1438.839|571218.306|7423848.605
8502.84|2620.24|568605.287|7428993.832
-2500.032|3457.767|558433.331|7433259.449

Mapinfo reference sytle is here: "Mine to MGA", 3008, 33,7, 117, 0, 0.9996, 500000, 10000000 , 7, 0.949288, -0.315744, 1814394.28, 0.315737, 0.94926, -7228957.16, -100000, -100000, 100000, 100000

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    How can we know? This is just the distance matrix: i.stack.imgur.com/a7qU7.png, between each point and the others, in both systems. The differences are not constant. We don't have a numerical method to know the custom projection and parameters. You need to know something about it. How were the points measured? How do you get their coordinates? – Gabriel De Luca Feb 11 at 4:41
  • From my understanding you can use the Proj4 or WKT and create a false Easting and Nothing from a known projection system. The points were surveyed. Is there any other parameters/information you need to know? – Garth Cooper Feb 11 at 4:57
  • If you know the projection system please include it in your post. – Gabriel De Luca Feb 11 at 21:21
  • Updated - it's in GDA94 / MGA zone 50 – Garth Cooper Feb 12 at 3:48
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    From MGA to Mine... I am trying with the following WKT pastebin.com/raw/iit4NN4Z, QGIS (must be 3.10.2) recognizes it as valid but then can't reproject the layer. Help from the developers is needed I think. This features are form PROJ.6. This is the link to the Affine Transformation: proj.org/operations/transformations/affine.html. This is for the pipelines: proj.org/usage/transformation.html#transformation-pipelines – Gabriel De Luca Feb 12 at 7:52

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