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GIS software such as arcGIS allows you to georeference a raster by marking specific points that have known coordinates. It will run a regression that reprojects your raster in such a way that minimizes the squared distance between these points on the raster and their "real" coordinates. (Good summary here.)

I'd like a way to do this in R. If the feature doesn't exist, I'd be willing to implement it myself. However, in order to do this, I need a way to apply an arbitrary polynomial transformation to a raster, using bilinear interpolation or a similar method. I'm aware that I can easily reproject a raster with a known projection and datum into a different projection and datum, but I need a capability that is more general.

Edit: Stack Overflow suggests I edit my answer to explain how this question is different from existing questions, but the existing answers deal with reprojection into a known coordinate system. I need to reproject into an arbitrary system, determined by the control points.

Dumb Political Scientist
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    I am not aware of a way, but I would be happy to add this to the raster package if you wrote it. – Robert Hijmans Jun 09 '16 at 05:20
  • http://neondataskills.org/R/Reproject-Raster-In-R/ – Hack-R Jun 09 '16 at 05:32
  • You're not aware of a way to use ground control points, or you're not aware of a way to apply an arbitrary transformation to a raster? – Dumb Political Scientist Jun 09 '16 at 20:32
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    Would the people who keep marking this as a duplicate please explain why they think it's a duplicate? The other answer says absolutely nothing about using control points, to start with. – Dumb Political Scientist Jun 11 '16 at 02:35
  • I agree that this is clearly not a duplicate. This question relates to reprojection to an *unspecified* coordinate system which is inferred from georefernced points. Other answers on SO relate to reprojection into a *known* coordinate system - a different matter entirely. – dww Jun 13 '16 at 20:31
  • Thanks; that's a good way to phrase the distinction and I'll edit accordingly. Do you know if there's any way to remove the "this question already has an answer" tag? – Dumb Political Scientist Jun 27 '16 at 18:50

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