Richard Gould a écrit :
> I'm giving a set of source points (image pixels) and destination points
> (world coordinates) to the WarpTransform2D class, and using that to
> create the WarpPolynomial object to perform the JAI operation, but the
> Warp that is created contains a strange affine transform. Although it is
> more than likely that I just don't quite understand what is going on.
WarpTransform2D is build on top of
javax.media.jai.WarpPolynomial.createWarp(...)
I noticed strange behavior when the amount of points is close to the required
minimum. It sound like that this method need slightly overdetermined set of
points in order to give good result.
> The Warp's affine transform:
> [[0.0, 0.0, 0.0], [0.0, 1.0, 0.0]]
>
> I would think that that would be the identity? The image returned by JAI
> is the same shape, but it is blank.
A line with only 0.0 values is suspect and is probably responsible for the
blank
image...
> Here is my test source code:
>
> src[0] = new Point(0,0);
> dest[0] = new DirectPosition2D(0, 0);
>
> src[1] = new Point(0, 24);
> dest[1] = new DirectPosition2D(0, 24);
>
> src[2] = new Point(24, 24);
> dest[2] = new DirectPosition2D(24, 24);
>
> src[3] = new Point(24, 0);
> dest[3] = new DirectPosition2D(24, 0);
I'm really not sure, but it may be worth to try the following:
* Provides some additional points
* Avoid to provides only points that are on the same line or
same columns (i.e. try to provides points that looks like
more random).
I really don't know if it will help; it is just a guess. In the referencing
module test suite, we create affine transform and quadratic transform from a
set
of 100 random points, and it work.
http://svn.geotools.org/geotools/trunk/gt/modules/library/referencing/src/test/java/org/geotools/referencing/operation/transform/WarpTransformTest.java
100 points is probably much more than needed; it should work with much less
points, but I don't know what the "real" minimum is. It seems to be more than
what is currently documented.
Martin
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