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

[Brian Case]

Chris,

Try passing gdalwarp -et 0.0

I am also suspicious of doing compression with the warp. you might want
to do that as a second step

Brian

On Wed, 2011-08-31 at 23:16 -0700, heng.feng wrote:
> 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
> 
> 
> 
> 
> 
> --
> View this message in context: http://osgeo-org.1803224.n2.nabble.com/GDALWARP-Chunk-Problem-Tiling-Effect-tp6749055p6749055.html
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