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

Jed Brown jed at 59A2.org
Sun May 1 08:13:59 EDT 2011

To clarify, what I'm looking for is exactly the inverse operation to
"gridding" as defined here:


This is much simpler and it's not difficult to write the low-level code
myself, but it seems quite strange to not have a high-level interface. Is
there really no interface, or am I just inadequate at reading the docs?

On Tue, Apr 26, 2011 at 01:24, Jed Brown <jed at 59a2.org> wrote:

> 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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