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From "Martin Desruisseaux (Jira)" <j...@apache.org>
Subject [jira] [Created] (SIS-497) ResamplingGrid should be incremental
Date Tue, 30 Jun 2020 10:36:00 GMT
Martin Desruisseaux created SIS-497:
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             Summary: ResamplingGrid should be incremental
                 Key: SIS-497
                 URL: https://issues.apache.org/jira/browse/SIS-497
             Project: Spatial Information Systems
          Issue Type: Task
          Components: Referencing
    Affects Versions: 1.1
            Reporter: Martin Desruisseaux


{{ResamplingGrid}} can accelerate raster reprojection by pre-computing source pixel coordinates
only in a few locations, then apply a bilinear interpolations between those locations. This
is the same strategy than the one applied by {{WarpGrid}} in Java Advanced Imaging.

In practice, tests suggest that {{ResamplingGrid}} indeed make raster reprojection faster
when the whole image is being reprojected. But it is slower if we prepare a reprojected image,
then query only a few tiles from it. The reason is that {{ResamplingGrid}} prepares a grid
of coordinates for the whole image, even if only a few tiles are requested later.

The proposed fix is to make {{ResamplingGrid}} incremental: apply it on a tile-by-tile basis
instead than for the whole image. A nice side-effect would be to detect when the transform
can be simplified to an affine transform on a tile-by-tile basis (current behavior requires
that simplification to apply to the whole image). Difficulties are:

* More difficult to determine in advance if {{PlanarImage.POSITIONAL_ACCURACY_KEY}} can provide
a "0.125 px" property value.
* May introduce redundant Jacobian matrix computations (matrices at tile corners computed
up to 4 times), unless we introduce a mechanism for saving previous computation results.




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