[gdal-dev] How to sample raster data at unstructured points?

[Jed Brown]

I have a bunch of unstructured points, typically quadrature nodes of an
unstructured mesh, and I want to sample a raster field at those points. I
have plenty of spatial locality, but not any specific regular structure.
Maybe I'm missing something, but I don't see an API for this direction.

There is GDALCreateTPSTransformer which would seem to be a reasonable way to
go from an unstructured mesh to a raster. But it's not easy to go the other
way since it would involve, e.g. defining a (bad) quadrature using the
raster and then do a Galerkin projection into the unstructured finite
element basis, then evaluate that basis at the unstructured quadrature
nodes. Alternatively, we could make tiny regular patches in the unstructured
grid and do lots of independent projections, but I worry that this would be
a performance issue.

Is there a recommended way to sample a raster field at unstructured points?
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