v.greedycolors - GRASS GIS manual

DESCRIPTION
EXAMPLE
SEE ALSO
AUTHOR

NAME

v.greedycolors - Create greedy colors for vector areas.

KEYWORDS

vector, color table

SYNOPSIS

v.greedycolors

v.greedycolors --help

v.greedycolors map=name [layer=string] [column=name] [--help] [--verbose] [--quiet] [--ui]

Flags:

--help: Print usage summary
--verbose: Verbose module output
--quiet: Quiet module output
--ui: Force launching GUI dialog

Parameters:

map=name [required]: Name of vector map; Or data source for direct OGR access
layer=string: Layer number or name; Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.; Default: 1
column=name: Name of attribute column; Default: greedyclr

DESCRIPTION
EXAMPLE
SEE ALSO
AUTHOR

DESCRIPTION

v.greedycolors assigns numbers to areas such that no two adjacent areas have the same number. At the same time, it tries to use as few numbers as possible. The numbers are stored in the attribute table, by default in the column "greedyclr" which is created if not existing. These numbers can then be used to assign RGB colors in a new column to be used with e.g. d.vect .

v.greedycolors works best if areas have unique categories. If multiple areas have the same category, the corresponding network of neighboring areas can become fairly complex, resulting in a larger number of greedy colors. If the purpose is to assign different colors to neighboring areas, irrespective of their category values, unique category values need to be assigned first, e.g. to a new layer with v.category.

There is always at least one optimal solution for greedy colors, using as few colors as possible. However, it is usually computationally intensive and not practical to search for an optimal solution. Therefore a good solution is aproximated by ordering the areas first, before assigning greedy colors. Here, the areas with the least neighbors are processed first.

EXAMPLE

Assigning greedy colors to county boundaries in the North Carolina sample dataset:

Make a copy of the data:

g.copy vect=boundary_county,my_boundary_county

Greedy colors

v.greedycolors map=my_boundary_county

Check number and frequency of greedy colors

db.select sql="select greedyclr,count(greedyclr) from my_boundary_county group by greedyclr"

gives

greedyclr|count(greedyclr)
1|262
2|351
3|302
4|11

four different colors were needed such that no two adjacent areas have the same color

Assign RGB colors:

v.db.addcolumn map=my_boundary_county column="GRASSRGB varchar(11)"

v.db.update map=my_boundary_county column=GRASSRGB value="127:201:127" where="greedyclr = 1"
v.db.update map=my_boundary_county column=GRASSRGB value="190:174:212" where="greedyclr = 2"
v.db.update map=my_boundary_county column=GRASSRGB value="253:192:134" where="greedyclr = 3"
v.db.update map=my_boundary_county column=GRASSRGB value="255:255:153" where="greedyclr = 4"

AUTHOR

Markus Metz, mundialis, Germany

SOURCE CODE

Available at: v.greedycolors source code (history)

Latest change: Thursday Mar 20 21:36:57 2025 in commit: 7286ecf7af235bfd089fb9b1b82fb383cf95f3fc