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NAME

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

KEYWORDS

raster, color table, cubehelix, seaborn

SYNOPSIS

r.colors.cubehelix
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]

Flags:

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

Parameters:

map=name[,name,...]
Raster map(s) to apply color table to
output=name
Name for the new color table rules file
start=float
The hue at the start of the helix
Options: 0-3
Default: 0
nrotations=float
Rotations around the hue wheel
Rotations around the hue wheel over the range of the color table
Options: 0-3
Default: 0.4
gamma=float
Gamma factor to emphasize darker (<1) or lighter (>1) colors
Options: 0-
Default: 1.0
hue=float
Saturation of the colors
Options: 0-1
Default: 0.8
light=float
Intensity of the lightest color in the color table
Options: 0-1
Default: 0.85
dark=float
Intensity of the darkest color in the color table
Options: 0-1
Default: 0.15
ncolors=integer
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

DESCRIPTION

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.

NOTES

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.

EXAMPLES

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.

REFERENCES

SEE ALSO

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

seaborn cubehelix_palette function documentation and an example

AUTHOR

Vaclav Petras, NCSU OSGeoREL

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

SOURCE CODE

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


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