[gdal-dev] gdalwarp different results (vrt vs direct)

[Stefan Ziegler]

Hi

We have a lot of aerial images. Each image has a size of 8000x8000 pixels
and the resolution is 12.5cm/pixel (-> 1 sqkm). They form a mosaic w/o any
gaps and overlaps. For transforming them into a new reference frame I'm
creating an vrt first and then using gdalwarp for the transformation (in a
for-loop). With this approach we can force the resulting images to have
bounding boxes with "nice" coordinates:

gdalwarp -s_srs "+proj=somerc +lat_0=46.952405555555555N
+lon_0=7.439583333333333E +ellps=bessel +x_0=600000 +y_0=200000
+towgs84=674.374,15.056,405.346 +units=m +units=m +k_0=1
+nadgrids=./chenyx06a.gsb" -t_srs "+proj=somerc +lat_0=46.952405555555555N
+lon_0=7.439583333333333E +ellps=bessel +x_0=2600000 +y_0=1200000
+towgs84=674.374,15.056,405.346 +units=m +k_0=1 +nadgrids=@null" -tr 0.125
0.125 -te 2611000 1233000 2612000 1234000 -co 'TILED=YES'  ortho2014.vrt
output.tif

The resulting image does have some strange artefacts, similar to a breaking
edge almost vertically through the whole image [1].

When using gdalwarp with the same -s_srs and -t_srs parameters for a single
image there is no breaking edge [2].

Any ideas what's going on?

I'm using gdal 1.11.

[1]: http://www.catais.org/tmp/gdalwarp_vrt.jpeg
[2]: http://www.catais.org/tmp/gdalwarp_direct.jpeg

best regards
Stefan
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