[gdal-dev] GDALWARP Chunk Problem (Tiling Effect)

[heng.feng]

Hi,

I have used the (OSGeo4W) GDALWARP command to warp some height data image
files (NTv2 transformation). When displaying one warped height data in our
own application, there appear to be visible tiles on the image and some
misalignments exist between those square tiles (chunks). 

After warping, I did make some conversion on the height data from the
original format (ERDAS Imagine) to another format, which can be accepted by
our own application. However, I think this tiling effect is not caused by
the format conversion, but most likely by something in the GDALWARP command.
The reason for saying this is that I have done the same format conversion on
the original height data without warping and there are no tiling effects at
all for the converted height data when shown in our application. As
attached, please see the two screenshots for the same area of the height
data being displayed in our application. One is with warping while the other
is without warping.

I seem to remember that the GDALWAP command does the chunk warping. Could
this be the reason why? 

The GDALWARP command I have been using is something like this:

gdalwarp --config GDAL_CACHEMAX 250 -wm 250 -co COMPRESS=LZW -co BIGTIFF=YES
-co TILED=YES -multi -overwrite -s_srs "+proj=tmerc +lat_0=0 +lon_0=12
+k=1.000000 +x_0=4500000 +y_0=0 +ellps=bessel +datum=potsdam
+nadgrids=c:\height \BETA2007.gsb,null +units=m +wktext" -t_srs "+proj=utm
+datum=WGS84 +zone=32" "c:\height\test.img" "c:\height\test.tif"

I have tried the GDALWARP command on the same height data by taking away all
the above command options and got the same tiling effect. Also I have
managed to open the warped height map data (tif format) in another GIS
application and could see the tiling effects as well although the effect is
not as visible as seen in our own application. I think this is because the
color interpretation type is gray in that warped height tif file. 

The other thing worth mentioning is: with the same warping and conversion
process, lower resolution height data (or much smaller height data) do not
seem to have such visible tiling effects.

Anyway, does anyone here have any clue about this? And is there any way to
get rid of the tiling effects in the warped height data?

Many thanks & BR,
Chris Feng





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