16.14. colormap

The colormap tool reads a DEM or some other single-channel image, and writes a corresponding color-coded image that can be used for visualization.

Usage:

colormap [options] <input DEM>

Example:

colormap --min -5 --max 10 image.tif

This will produce image_CMAP.tif, with the “hottest” color corresponding to pixel values at least 10, and the “coolest” color representing pixel values less than or equal to -5.

To create a hillshaded (Section 16.27) colormap of a DEM, run:

colormap --hillshade -e 25 -a 300 dem.tif -o color-shaded.tif

Alternatively, run:

hillshade -e 25 -a 300 dem.tif -o shaded.tif
colormap dem.tif -s shaded.tif -o color-shaded.tif

The second approach can incorporate any type of grayscale image as a multiplier to the colorized image.

See Section 6.2 for a discussion of ASP’s visualization tools, including this one.

To add a colorbar and axes, use stereo_gui (Section 16.67.5).

Fig. 16.2 Example of images produced with the following colormaps (left to right, and top-down): binary-red-blue (default), jet, black-body, viridis, kindlmann, cubehelix, plasma, inferno, rainbow, turbo (source1, source2).

16.14.1. Using your own colormap

Both this tool and stereo_gui (Section 16.67) accept a user-defined colormap. It should be in a file named, for example, mycolormap, and can be passed to these tools via --colormap-style mycolormap. Such a file must be in plain text, with four columns having on each row a floating point number (increasing from 0 to 1), then 3 integers between 0 and 255, corresponding to the RGB components of a color.

Here’s an example Python code which creates a custom colormap, by exporting it from a matplotlib colormap:

#!/usr/bin/python

from matplotlib import cm

# colormap name goes here, e.g., 'turbo'
cmap = cm.turbo
num = cmap.N
for i in range(num):
   rgba = cmap(i)
   print(i / float(num - 1),
         round(255 * rgba[0]),
         round(255 * rgba[1]),
         round(255 * rgba[2]))

Save this script as export_colormap.py, and run it as:

python ~/bin/export_colormap.py > mycolormap

16.14.2. Command-line options for colormap

-o, --output-file <filename>

Specify the output file.

--colormap-style <string (default=”binary-red-blue”)>

Specify the colormap style. Options: binary-red-blue (default), jet, black-body, viridis, kindlmann, cubehelix, plasma, inferno, rainbow, turbo. Or specify the name of a file having the colormap, on each line of which there must be a normalized or percentage intensity and the three integer RGB values it maps to.

--nodata-value <arg>

Remap the DEM default value to the min altitude value.

--min <arg>

Minimum height of the color map.

--max <arg>

Maximum height of the color map.

--moon

Set the min and max height to good values for the Moon.

--mars

Set the min and max height to good values for Mars.

-s, --shaded-relief-file <filename>

Specify a shaded relief image (grayscale) to apply to the colorized image. For example, this can be a hillshaded image.

--hillshade

Create a hillshaded image first, then incorporate it in the colormap. This is equivalent to using an external file with the --shaded-relief-file option.

-a, --azimuth <number-in-degrees (default: 300)>

Sets the direction that the light source is coming from (in degrees). Zero degrees is to the right, with positive degrees counter-clockwise. To be used with the --hillshade option.

-e, --elevation <number-in-degrees (default: 20)>

Set the elevation of the light source (in degrees). To be used with the --hillshade option.

--legend

Generate an unlabeled legend, will be saved as legend.png.

--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.