Re: [Geotools-devel] Envelope reprojection issues on stereographic projectsion

[Olaf D. <ola...@br...>]

Martin, =20

interesting discussion indeed. The problem looks very similar to ours
described in

http://www.nabble.com/Still-problems-with-reprojecting-raster-data-p9689563=
.html
http://www.nabble.com/Still-problems-with-reprojecting-raster-data-p9689563=
.html=20

We found a workaround in the way that we calculate our target envelope
ourselves before the rendering, and then put this envelope in a modified
StreamingRenderer and GridCoverageRenderer, which just hand this unchanged
envelope over to be used in Resampler2D. Originally, the target envelope wa=
s
determined there by calling 'CRSUtilities.transform(..., sourceEnvelope).
Moreover, we skipped the cropping in GridCoverageRenderer done by
'CRSUtilities.transform(deviceCRSToGCCRSTransform,destinationEnvelope)',
which already produced a wrong 'destinationEnvelopeInSourceGCCRS' when a
pole is included.
Of course I'm not sure if we might have missed something (it was hard to
understand all the rendering stuff), but at least we now obtain reasonable
raster images for AzimuthalEquidistant and Gnomonic projections including a
pole.

Cheers,
Olaf


Martin Desruisseaux-2 wrote:
>=20
> Andrea Aime a =C3=A9crit :
>> In this case the singularity is the south pole, whose latitude is
>> determined, but longitude is not. When you have it, you should add
>> the -180,180 range to envelope longitudes (or I'm missing something)?
>=20
> Longitude would be tested too, like every bounded axis (no matter which
> axis it
> is). In the particular case of South Pole, the longitude is irrelevant,
> but this
> is just a particular case. Generally speaking, we have a choice:
>=20
> Testing  (-180, -90), (180, -90), (-180, 90), (180, 90)
>=20
> or testing (-180, centerY), (180, centerY), (centerX, -90), (centerX, 90)=
.
>=20
> Where (centerX, centerY) are relative to the initially transformed
> envelope. I
> tend toward the later. It make no difference for polar projections, but
> may make
> a difference for the 180=C2=B0 longitude bounds. Consider a MercatorProje=
ction
> where
> the transformed envelope is between 20=C2=B0N and 40=C2=B0N. If we try to=
 project
> (-180,
> 90) and its friends, we will get a TransformException because Mercator
> projection is not supported at the pole. If we try to project (-180,
> centerY)
> instead, we will get a valid point. If this point is inside the source
> envelope
> because this envelope overlaps the 180=C2=B0 longitude, the transformed
> envelope will
> be expanded on the full (-180 to 180) width. This is quite large, but at
> least
> it is correct, better than actual behavior which return a completly wrong
> target
> envelope when the source envelope overlaps the 180=C2=B0 longitude.
>=20
> =09Martin
>=20
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>=20
>=20

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