gdalwarp, cutline and postgis

Question

I can not figure out how I directly can read a polygon into gdawarp's -cutline argument.

My current approach is:

ogr2ogr -f "ESRI Shapefile" mydata.shp PG:"user=myuser dbname=gisdb" -sql "select * from polys where id='12345'"
and then I run

gdalwarp -cutline mydata.shp in.tif out.tif

How could I skip the step with the shapefile?

Thanks in advance for any hints

Answer 1

If you're using GDAL 1.8.0 (which I recommend because it adds a number of useful features), you can use:

gdalwarp -cutline "PG:dbname=gisdb" -csql 'select * from polytest where id=1' -crop_to_cutline -of GTiff -srcnodata -9999 -dstnodata -9999 src.tif dest.tif

Note the "-crop_to_cutline" parameter.

With gdalwarp, I have found it always pays to use -srcnodata and -dstnodata explicitly, otherwise it'll fill the nodata areas with 0/black which quite often is a valid value.