Smathermather's Weblog

Remote Sensing, GIS, Ecology, and Oddball Techniques

Batch processing resampling of DEMs

Posted by smathermather on January 4, 2010

Yet again, working with that Ohio DEM dataset, I need some reduced resolution versions of the 2.5 foot DEMs.  At a grand total of ~600 DEMs for a given county, it was time to batch, this time in Windows Command prompt.  The neat thing is the variable substitution in the for-in-do command in the command prompt, where, e.g. for a file variable %f, the file name, minus extension can be invoked with %~nf.  As I write this,  I realize that I didn’t strictly need that variable for this dataset, as they were ESRI Grids, so they have no extension to trim off… .  Hehe.  I think I was being stupidly clever.  But, well, trim off the /D flag, and you can use this with any file extension… .  So, ya.  This is the more generic solution… .

I use bilinear resampling below for each tier from half the resolution.  Why bilinear when there are fancy resampling methods available?  I trust bilinear to do exactly what I want, and that is create an averaged tier that can be overlayed with the original data 100% (knock on wood… .).  I can quantify it’s behavior at each tier.  In other words, I’m fussy, and I understand bilinear, and haven’t invested the time to find out if I like anything else… .

for /D %f in (n*) do gdalwarp -tr 5 5 -r bilinear %f resampled\%~nf_05.tif
for /D %f in (n*) do gdalwarp -tr 10 10 -r bilinear resampled\%~nf_05.tif resampled\%~nf_10.tif
for /D %f in (n*) do gdalwarp -tr 20 20 -r bilinear resampled\%~nf_10.tif resampled\%~nf_20.tif
for /D %f in (n*) do gdalwarp -tr 40 40 -r bilinear resampled\%~nf_20.tif resampled\%~nf_40.tif
for /D %f in (n*) do gdalwarp -tr 80 80 -r bilinear resampled\%~nf_40.tif resampled\%~nf_80.tif
for /D %f in (n*) do gdalwarp -tr 160 160 -r bilinear resampled\%~nf_80.tif resampled\%~nf_160.tif

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