Re: [Geotools-gt2-users] clip grid coverage

[Martin D. <mar...@no...>]

Tom Howe a =E9crit :
> I need to take a grid coverage and clip it based on a Polygon.  My
> plan was to just loop through the cells of the coverage and check to
> see if polygon.contains(point) from the cell.  If so,, then add the
> value to a new coverage.  I was thinking about constraining this
> further by only checking the cells in that are contained in the
> bounding box of the polygon.  Any thoughts on if this is the best way
> to approach the problem or any suggestions on how to do this?  I can
> brute force it, but I wanted to see if anyone had better suggestions.

If the polygon is actually a rectangle, the "resample" operation whould=20
be quite efficient (it should maps to a JAI's "Crop" operation):

GridRange    newRange    =3D new GeneralGridRange(...);
GridGeometry newGeometry =3D new GridGeometry2D(newRange,=20
(MathTransform)null);
Coverage newCoverage =3D Operations.resample(source, null, newGeometry, n=
ull);

For more complex geometry, we don't have yet any explict API in=20
Geotools. But the most efficient way may be to use the JAI operations.=20
I'm not sure which JAI operation is the most appropriate, since I have=20
not yet investigated this problem. Maybe the "AndConst" operation with=20
some javax.media.jai.ROIShape inferred from yours Geometry. If an=20
appropriate JAI operation is found, we can get the RenderedImage using=20
GridCoverage2D.getRenderedImage(), apply the JAI operation and recreate=20
the GridCoverage2D with the operation result.

Actually I don't really have an easy way to suggest right now...

	Martin.