[jira] [Commented] (SIS-497) ResamplingGrid should be incremental

["Martin Desruisseaux (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SIS-497?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17148525#comment-17148525 ] 

Martin Desruisseaux commented on SIS-497:
-----------------------------------------

After this issue is fixed, commit [0420f26|https://github.com/apache/sis/commit/0420f26b29a756908f37df09fbe0b5940931ad46] should be reverted.

> ResamplingGrid should be incremental
> ------------------------------------
>
>                 Key: SIS-497
>                 URL: https://issues.apache.org/jira/browse/SIS-497
>             Project: Spatial Information Systems
>          Issue Type: Task
>          Components: Features
>    Affects Versions: 1.1
>            Reporter: Martin Desruisseaux
>            Priority: Major
>
> {{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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