Frank,
I created a ticket with the same description as below:
http://trac.osgeo.org/gdal/ticket/4907
My test cases are from self-made Raw-VRTs, so I have no immediate
reproducable test image/script to attach. However, if useful, I can
construct an example to attach in a couple of days.
Thank you for looking into this.
Best regards from Knut-Frode
Den 26.11.2012 22:14, skrev Frank Warmerdam:
On 12-11-26 12:11 PM, Knut-Frode Dagestad wrote:
Dear list,
Warping datasets with geolocation arrays works fine if the arrays have
the same
size as the other raster bands. However, if the geolocation arrays are
much
smaller, the quality is very bad.
Say I have a 2000x2000 px dataset with 100x100 px sized geolocation
arrays.
Then a warped image have only 200x200 blocks of identical values, even
if the
size of the warped image is much larger. If I change the interpolation
algorithm (neareast, cubic...) the values change slightly, but the
real output
resolution remains low. This is the same whether using Python API or
gdalwarp.
As a workaround I convert the geolocation arrays to GCPs. This gives
decent
warping quality, but is a bit awkward.
Is this the expected behavior of the present implementation of
geolocation
arrays in GDAL?
Knut-Frode,
The intention is that the geolocation information will be linearly
interpolated from the geolocation array. However, I gather you are not
seeing that effect.
Looking at the "backmap" it seems that this linear interpolation is not
being done, even though it is (after a fashion) in the forward case
transformation case. I'd appreciate it if you could submit a bug on
this issue, and I'll look into correcting it. It is a pretty serious
error.
Best regards,
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