Mini GDAL tip of the day:

gdalwarp, especially in combination with gdal_merge, is a powerful tool for doing all sorts on nice aggregation (read: mosaic’ing) of spatial raster data.  Unfortunately, at least with a google search, there’s very little to be found on demonstrating the use of queries in conjunction with cutlines, probably because in general these queries are not difficult to figure out.

In a previous post, I demonstrated using this to stitch together USGS quads.  I found out when I tried to run this code on a Linux machine, the command like code was a little different.  Instead of:

gdal_merge -o usgs_merge.tif -createonly input1.tif input2.tif ...
gdalwarp -cutline quadrangle_index_24k.shp -cwhere "quadname_ = West_View" West_View.tif usgs_merge.tif

I found I needed some extra single quotes to get my string literal to not be interpreted as a field:

gdalwarp -cutline quadrangle_index_24k.shp -cwhere "quadname_ = 'West_View'" West_View.tif usgs_merge.tif

Ah, that’s better.  Now I have a nice big mosaic of DEMs for my region with perfect cuts where the overlaps used to be.  (The change is hard to see– look for single quotes around West_View in “quadname_ = ‘West_View'”)