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r.colors.cubehelix - Create or apply a cubehelix color table to a GRASS raster map


raster, color table, cubehelix, seaborn


r.colors.cubehelix --help
r.colors.cubehelix [-dngae] [map=name[,name,...]] [output=name] [start=float] [nrotations=float] [gamma=float] [hue=float] [light=float] [dark=float] [ncolors=integer] [--overwrite] [--help] [--verbose] [--quiet] [--ui]


Generate discrete color table
Generate discrete (interval) color table instead of a continuous one
Reverse the order of colors (invert colors)
If set, the color table will go from dark to light
Logarithmic scaling
Logarithmic-absolute scaling
Histogram equalization
Allow output files to overwrite existing files
Print usage summary
Verbose module output
Quiet module output
Force launching GUI dialog


Raster map(s) to apply color table to
Name for the new color table rules file
The hue at the start of the helix
Options: 0-3
Default: 0
Rotations around the hue wheel
Rotations around the hue wheel over the range of the color table
Options: 0-3
Default: 0.4
Gamma factor to emphasize darker (<1) or lighter (>1) colors
Options: 0-
Default: 1.0
Saturation of the colors
Options: 0-1
Default: 0.8
Intensity of the lightest color in the color table
Options: 0-1
Default: 0.85
Intensity of the darkest color in the color table
Options: 0-1
Default: 0.15
Number of colors in the color table
Number of color intervals in a discrete color table with -d
Options: 2-
Default: 6

Table of contents


The r.colors.cubehelix module generates a cubehelix color table and assigns it to given raster map if requested. The color table is generated using seaborn Python package. Several pararameters are available to control the cubehelix. When option map is specified r.colors.cubehelix assigns the color rules to the given raster map. The color tables is always stratched based on the range of values of the map

Depending on the use case, it may be advantageous to use the -d to discretize the color table into intervals.


This module depends on seaborn which needs to be installed on your computer. Use your Python package manager (e.g. pip) or distribution package manager to install it.


Creating a color table as GRASS color rules

We do 0.6 rotation around the axis and use discrete (interval) color table rather than the standard continuous. If we don't specify output file, it is printed to standard output:
r.colors.cubehelix -d ncolors=5 nrotations=0.6
0.000% 218:222:192
20.000% 218:222:192
20.000% 198:166:136
40.000% 198:166:136
40.000% 173:108:112
60.000% 173:108:112
60.000% 119:61:98
80.000% 119:61:98
80.000% 48:28:59
100.000% 48:28:59

Setting color table for a raster map

Now we set several different color tables for the elevation raster map from the North Carolina sample dataset. We use continuous and discrete color tables (gradients). The color tables ae stretched to fit the raster map range.
r.colors.cubehelix -d ncolors=8 nrotations=0.6 map=elevation
We can display legend:
d.legend raster=elevation labelnum=10 at=5,50,7,10
Here we set continuous color table with more colors
r.colors.cubehelix nrotations=1.4 start=4 map=elevation

Setting color table for a vector map

First we create a text file with color rules:
r.colors.cubehelix -i rot=0.6 output=cubehelix.txt
Then we set color table for the vector to the rules stored in a file:
v.colors map=points rules=cubehelix.txt
Color table for 3D raster map can be set in the same way.



r.colors, v.colors, r3.colors, r.cpt2grass, r.colors.matplotlib

seaborn cubehelix_palette function documentation and an example


Vaclav Petras, NCSU OSGeoREL

Last changed: $Date: 2016-06-09 09:40:22 +0200 (Thu, 09 Jun 2016) $


Available at: r.colors.cubehelix source code (history)

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