Merge rasters
gdal_warp
You can use gdalwarp to merge the images together:
gdalwarp input1.tif input2.tif merged.tif
where:
- input1.tif input2.tif ...: the input files
- merged.tif: the merged output
Give it a try here:
gdalwarp sf_4269-nobhill.tif sf_4269-chinatown.tif sf_4269-downtown.tif sf-merged.tif
Or, to preserve nodata values:
gdalwarp input1.tif input2.tif merged.tif -srcnodata