16.23. geodiff

The geodiff program takes as input two DEMs (or a DEM and a CSV file, with the latter in the same format as used for pc_align and point2dem), and subtracts the second from the first. The grid used is the one from the first DEM, so the second one is interpolated into it using bilinear interpolation (when one file is a CSV, the grid from the other one, the DEM, is used). The tool can also take the absolute difference of the two DEMs.

It is important to note that the tool is very sensitive to the order of the two DEMs, due to the fact that the grid comes from the first one. Ideally the grid of the first DEM would be denser than the one of the second.

Usage:

geodiff [options] <dem1> <dem2> [ -o output_file_prefix ]

Example with two DEMs (when computing an absolute difference):

geodiff --absolute dem1.tif dem2.tif -o run

This will create run-diff.tif.

The colormap program (Section 16.14) can be used to colorize the difference image.

Example with a DEM and a CSV file:

geodiff dem1.tif file.csv                         \
  --csv-format '1:lon 2:lat 3:height_above_datum' \
  -o run

Command-line options for geodiff:

-o, --output-prefix <filename>

Specify the output prefix.

--absolute

Output the absolute difference as opposed to just the difference.

--float

Output using float (32 bit) instead of using doubles (64 bit).

--csv-format <string>

Specify the format of input CSV files as a list of entries column_index:column_type (indices start from 1). Examples: 1:x 2:y 3:z (a Cartesian coordinate system with origin at planet center is assumed, with the units being in meters), 5:lon 6:lat 7:radius_m (longitude and latitude are in degrees, the radius is measured in meters from planet center), 3:lat 2:lon 1:height_above_datum, 1:easting 2:northing 3:height_above_datum (need to set --csv-proj4; the height above datum is in meters). Can also use radius_km for column_type, when it is again measured from planet center.

--csv-proj4 <proj string>

The PROJ.4 string to use to interpret the entries in input CSV files, if those files contain Easting and Northing fields. If not specified, it will be borrowed from the DEM.

--nodata-value <float (default: -32768)>

The no-data value to use, unless present in the DEM geoheaders.

--threads <integer (default: 0)>

Select the number of threads to use for each process. If 0, use the value in ~/.vwrc.

--cache-size-mb <integer (default = 1024)>

Set the system cache size, in MB.

--tile-size <integer (default: 256 256)>

Image tile size used for multi-threaded processing.

--no-bigtiff

Tell GDAL to not create bigtiffs.

--tif-compress <None|LZW|Deflate|Packbits (default: LZW)>

TIFF compression method.

-v, --version

Display the version of software.

-h, --help

Display this help message.