r.colors.cubehelix - GRASS GIS manual

NAME

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

KEYWORDS

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

DESCRIPTION
NOTES
EXAMPLES
REFERENCES
SEE ALSO
AUTHOR

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

Green, D. A., 2011, A colour scheme for the display of astronomical intensity images, Bulletin of the Astronomical Society of India, 39, 289.

AUTHOR

Vaclav Petras, NCSU OSGeoREL

SOURCE CODE

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