Monday, March 31, 2014

Identifying digital elevation model files with erroneous elevations in batch

A DEM file
Recently I had to identify ESRI ArcGrid ASCII files of digital elevation models with very low elevation values (below zero). If I had one or two files, then I could easily open up the file in Global Mapper or Saga GIS. But there were several hundred DEMs, which made that impractical. Luckily the free open source software GDAL has a utility gdalinfo that can generate statistics about a DEM in batch. The following example shows how to use gdalinfo to look for extreme low (or high) spikes in elevation.

  1. Open up a Windows Command Prompt.
  2. Type in the following:

    C:> gdalinfo -stats inputDEM.asc > output.txt

    Note: to append to an output file, use double ">" as below.

    C:> gdalinfo -stats inputDEM.asc >> output.txt

    Note II: For hundreds of files, simply put these commands into a batch script.
  3. Open up the output file e.g. output.txt in a text editor. Find the statistical values - minimum, maximum that are above or below the valid elevation ranges to identify the DEM files with erroneous values.

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