16.25. geodiff

The geodiff program takes as input two DEMs, or a DEM and a CSV file, and subtracts the second from the first. The grid is 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 DEM is used, regardless of the order of inputs.

It is important to note that geodiff 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 ]

16.25.1. Examples

Take the absolute difference of two DEMs:

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

This will create run-diff.tif.

The stereo_gui program (Section 16.67.5) can colorize on-the-fly and display the difference image. The colormap program (Section 16.14) can write a colorized image.

Take the difference of a DEM and a CSV file:

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

The produced run-diff.csv file can be visualized and colorized with stereo_gui (Section 16.67.6), as:

stereo_gui --colorbar run-diff.csv

This program can also overlay the difference on top of the DEM.

16.25.2. See also

The image_calc program (Section 16.33) can perform many operations on images, as long as they are the same size (use gdalwarp, Section 16.24, to convert images to the same extent and georeference).

16.25.3. Command-line options

-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.