16.26. 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 ]
16.26.1. 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 16.70.5) 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 16.70.6), as:
stereo_gui --colorbar run-diff.csv
This program can also overlay the difference on top of the DEM.
16.26.2. See also¶
The image_calc
program (Section 16.34) can perform many operations on
images, as long as they are the same size (use gdalwarp
,
Section 16.25, to convert images to the same extent and georeference).
16.26.3. Command-line options¶
- -o, --output-prefix <filename>
Specify the output prefix.
- --absolute
Output the absolute difference as opposed to just the difference.
- --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-srs
; the height above datum is in meters). Can also use radius_km for column_type, when it is again measured from planet center.- --csv-srs <proj string>
The PROJ or WKT 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.
- --float
Output using float (32 bit) instead of using doubles (64 bit). This is now the default, and this option is obsolete.
- --tif-compress <None|LZW|Deflate|Packbits (default: LZW)>
TIFF compression method.
- -v, --version
Display the version of software.
- -h, --help
Display this help message.