[gdal-dev] Re: gdal_retile and nodata

acangi aca at ngi.be
Tue May 25 05:09:55 EDT 2010

Back from week-end, sorry for interrupting the conversation.

I tried setting a -a_nodata 255 value before creating the pyramid, the
result is exactly the same as with black nodata or without a nodata value.
The nodata value of the original geotiffs is ignored.

> First an image is created, large enough to hold the tile and its  
> neighbors from level x-1
Is it possible this image has a black background color ?

> Third, the scaling takes place.
I guess the black background is interpolated with the border data and
produces nearly black pixels.

> The problem is, sometimes neighbors are missing, right ?
Right : my source data is not a rectangle.

> Do you have this problem already at level 1 or beginning with level 2 ?
Curiously, it starts at level 3. At levels 0, 1 and 2, the black remains

> Do you start from one big image or an already tiled image ?
My source data is made of several geotiff images.

In the past, I generated the same pyramid and didn't have this problem. The
parameters that changed are : 
 -pyramidOnly in the past, now no more
 -ps 10000 10000 in the past, now 4096 4096
 -co COMPRESS="LZW" in the past, "JPEG" now
 - GDAL 1.6.0 in the past, now GDAL 1.7.2

The command I use now is :
gdal_retile.py -targetDir ../pyramid4096/ -levels 12 -v -s_srs
/mnt/webgisdata/geoserver/config/3812.prj -ps 4096 4096 -r bilinear -co
"COMPRESS=JPEG" -co "TILED=YES" -co "INTERLEAVE=PIXEL" -tileIndex orthocol
-tileIndexField location *.tif &

I gave a shot with LZW compression and the problem is gone away. But the
output data is 4 GB instead of 800 MB with JPEG compression. 

Do you think I should use LZW compression ?
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