3.-Joinning the tiles.
We're going to use gdal_merge for joinning the tiles, it's a console apllication (a command) for joinning raster datasets. I you type:
you will get a lot of information about this command, but I'm just getting to the meat of the matter:
If we have four tiles files srtm_36_04.tif, srtm_36_05.tif, srtm_37_04.tif y srtm_37_05.tif; you can join them typping:
After -o comes the name of the output file, after that comes the names of the files, space sepparated; though the desired output format is the same that the standard (GeoTiff) we're not using the -of option.
gdal_merge -o mosaico.tif srtm_36_04.tif srtm_36_05.tif srtm_37_04.tif srtm_37_05.tif
For cropping we are going to use gdalwarp.
after the -te option you must add the area coordinates
gdalwarp -te 626680 4191038 815725 4519394 mosaico.tif mosaico_rer.tif