today I needed to merge some of the map tiles described here:
but most of my programs failed. SAGA GIS is able to do it, but in this case it needs to manuallly import every single tile and finally had problems to export such a big file.
When using SAGA gdal export, then the colors were strange - a lot of purple instad of green etc. I found an advice how to do it via cmd with gdal_merge and generated filelist using:
Microsoft Windows XP [Verze 5.1.2600] (C) Copyright 1985-2001 Microsoft Corp. C:\WINDOWS>cd C:\D\EDU_ETE_mapy_zony\ETE_map_tiles\BW C:\D\EDU_ETE_mapy_zony\ETE_map_tiles\BW>gdal_merge -o merged.tif --optfile filelist.txt
but the output colors were also bad. I tried to convert all images with IrfanView to BW only images (not grayscale), but then is something wrong as the gdal output is black only.
there is probably one problem - when merging, gdal says:
Warning 1: TIFFReadDirectory:Unknown field with tag 33918 (0x847e) encountered Warning 1: TIFFFetchNormalTag:ASCII value for tag "GeoASCIIParams" does not end in null byte
SAGA reported something similars but I was able to get normal colors using "Force true colors" option, so I do not know how important is it.
does anybody have an idea to solve this? The correct color map would be nice but for most common use the 2bit (B-W) is enough (map is often used as background layer).