[Gdal-dev] Flashy colors in a pyramid

acangi aca at ngi.be
Wed Aug 19 03:51:37 EDT 2009

Hello list,

I created a pyramid of aerial photos using gdal_retile.py and now see there
are strange zones in the pyramid. I'm trying to understand why I got this
strange results and how I can fix it (Bombing the area to make sure it looks
like what I have ?). Description :
1. The command I used was gdal_retile.py -targetDir pyramid/ -levels 12
-pyramidOnly -v -s_srs /path/to/prjs/3812.prj -ps 10000 10000 -r bilinear
orthocol -tileIndexField location /path/to/source/files/*.tif &
2. In the source files, I see nothing special. The tiles in this area look
like the other ones.
3. On the first (generated) level of the pyramid, I see a small area (alias
SMALL_SQUARE : 256m x 256m) in blue :
4. On the next levels of the pyramid, a black rectangle 512m x 256m is now
visible where SMALL_SQUARE was : 
and the area corresponding to the first level tile containing SMALL_SQUARE
(alias BIG_SQUARE : 10000m x 10000m) is in green : 
5. I view the pyramid in geoserver, the tiles look like they are on disk,
except at the first level, geoserver doesn't show me the full SMALL_SQUARE,
only parts of it. In geoserver logs, I find nothing very interesting, it all
looks the same whether or not I'm looking at BIG_SQUARE.
6. If I set OutputTransparentColor to #000000 (the background color),
BIG_SQUARE is now invisible (in geoserver)

So, my questions are :
Why did it happen ? I suppose it's just a random error...
How can I fix it ? Is there any way other than rebuilding the whole pyramid

Any idea is welcome,

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