colourmap {spatstat.geom}

Colour Lookup Tables

Description

Create a colour map (colour lookup table).

Usage

colourmap(col, ..., range=NULL, breaks=NULL, inputs=NULL, gamma=1)

Arguments

col

Vector of values specifying colours

...

Ignored.

range

Interval to be mapped. A numeric vector of length 2, specifying the endpoints of the range of values to be mapped. Incompatible with breaks or inputs.

inputs

Values to which the colours are associated. A factor or vector of the same length as col. Incompatible with breaks or range.

breaks

Breakpoints for the colour map. A numeric vector of length equal to length(col)+1. Incompatible with range or inputs.

gamma

Exponent for the gamma correction, when range is given. A single positive number. See Details.

Details

A colour map is a mechanism for associating colours with data. It can be regarded as a function, mapping data to colours.

The command colourmap creates an object representing a colour map, which can then be used to control the plot commands in the spatstat package. It can also be used to compute the colour assigned to any data value.

The argument col specifies the colours to which data values will be mapped. It should be a vector whose entries can be interpreted as colours by the standard R graphics system. The entries can be string names of colours like "red", or integers that refer to colours in the standard palette, or strings containing six-letter hexadecimal codes like "#F0A0FF".

Exactly one of the arguments range, inputs or breaks must be specified by name.

• If inputs is given, then it should be a vector or factor, of the same length as col. The entries of inputs can be any atomic type (e.g. numeric, logical, character, complex) or factor values. The resulting colour map associates the value inputs[i] with the colour col[i]. The argument col should have the same length as inputs.

• If range is given, then it determines the interval of the real number line that will be mapped. It should be a numeric vector of length 2. The interval will be divided evenly into bands, each of which is assigned one of the colours in col. (If gamma is given, then the bands are equally spaced on a scale where the original values are raised to the power gamma.)

• If breaks is given, then it determines the precise intervals of the real number line which are mapped to each colour. It should be a numeric vector, of length at least 2, with entries that are in increasing order. Infinite values are allowed. Any number in the range between breaks[i] and breaks[i+1] will be mapped to the colour col[i]. The argument col should have length equal to length(breaks) - 1.

It is also permissible for col to be a single colour value, representing a trivial colour map in which all data values are mapped to the same colour.

The result is an object of class "colourmap". There are print and plot methods for this class. Some plot commands in the spatstat package accept an object of this class as a specification of the colour map.

The result is also a function f which can be used to compute the colour assigned to any data value. That is, f(x) returns the character value of the colour assigned to x. This also works for vectors of data values.

Value

A function, which is also an object of class "colourmap".

Author(s)

Adrian Baddeley [e-mail], Rolf Turner [e-mail] and Ege Rubak [e-mail].

See Also

The plot method plot.colourmap.

See the R help file on colours for information about the colours that R recognises, and how to manipulate them.

To make a smooth transition between colours, see interp.colourmap. To alter individual colour values, see tweak.colourmap. To extract or replace all colour values, see colouroutputs.

See also restrict.colourmap.

See colourtools for more tools to manipulate colour values.

See lut for lookup tables.

Examples

  # colour map for real numbers, using breakpoints
  cr <- colourmap(c("red", "blue", "green"), breaks=c(0,5,10,15))
  cr
  cr(3.2)
  cr(c(3,5,7))
  # a large colour map
  co <- colourmap(rainbow(100), range=c(-1,1))
  co(0.2)
  # colour map for discrete set of values
  ct <- colourmap(c("red", "green"), inputs=c(FALSE, TRUE))
  ct(TRUE)