Ralf,<br><br>Your tif files seem to use color tables. You may be able to edit the color table to represent RGBA instead of RGB with A value set to 0 for nodata and 1 elsewhere. I don't know much about handling the color tables.<br>
<br>If you don't want to deal color tables, use the -expand option in gdal_translate.<br>First use "-expand rgb" to create RBG tiffs. Then use gdalbuildvrt with -srcnodata and -addalpha options. Finally, convert it All.tif using gdal_translate.<br>
<br><div class="gmail_quote">On Mon, Feb 8, 2010 at 5:43 PM, Ralf Wagner <span dir="ltr"><<a href="mailto:rpw@globema.pl">rpw@globema.pl</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Unfortunately I have absolutely no idea how to deal with this transparency problem - all my trials failed.<br>
I am experimenting on four properly referenced GeoTiff, overlapping files with white margins.<br>
My (temporary) goal was to obtain ONE GeoTIFF file from these FOUR source files - but, of course, without white margins between them.<br>
So, first I created VRT file from my source GeoTiffs:<br>
<br>
gdalbuildvrt -srcnodata "255 255 255" All.vrt Ac3.tif Ac4.tif Ca1.tif Ca2.tif<br>
<br>
and then GeoTiff from this VRT file:<br>
<br>
gdal_translate -of GTiff All.vrt All.tif<br>
<br>
But white stripes still existed. Also, additional step of creating separate VRT files for each GeoTiff file and using these files as components for "All.vrt" didn't help. Messing around with -vrtnodata, -hidenodata etc. didn't help also. Using -addalpha option causes warning during destination GeoTiff file generation: "Unable to export color table to GeoTIFF file" and resulting file is broken.<br>
<br>
So, I am stuck...<br>
<br>
Do you have any idea what can I try next?<br>
<br>
Best regards,<br><font color="#888888">
Ralf Wagner<br>
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</font></blockquote></div><br><br clear="all"><br>-- <br>Best regards,<br>Chaitanya kumar CH.<br>/tʃaɪθənjə/ /kʊmɑr/ <br>+91-9848167848<br>17.241582N 80.142635E<br>