stretch: Stretch

In terra: Spatial Data Analysis

Stretch

Description

Linear or histogram equalization stretch of values in a SpatRaster.

For linear stretch, provide the desired output range (minv and maxv) and the lower and upper bounds in the original data, either as quantiles (minq and maxq, or as cell values (smin and smax). If smin and smax are both not NA, minq and maxq are ignored.

For histogram equalization, these arguments are ignored, but you can provide the desired scale of the output and the maximum number of cells that is used to compute the histogram (empirical cumulative distribution function).

Usage

## S4 method for signature 'SpatRaster'
stretch(x, minv=0, maxv=255, minq=0, maxq=1, smin=NA, smax=NA,
		histeq=FALSE, scale=1, maxcell=500000, filename="", ...)

Arguments

x	SpatRaster
minv	numeric >= 0 and smaller than maxv. lower bound of stretched value
maxv	numeric <= 255 and larger than maxv. upper bound of stretched value
minq	numeric >= 0 and smaller than maxq. lower quantile bound of original value. Ignored if smin is supplied
maxq	numeric <= 1 and larger than minq. upper quantile bound of original value. Ignored if smax is supplied
smin	numeric < smax. user supplied lower value for the layers, to be used instead of a quantile computed by the function itself
smax	numeric > smin. user supplied upper value for the layers, to be used instead of a quantile computed by the function itself
histeq	logical. If TRUE histogram equalization is used instead of linear stretch
scale	numeric. The scale (maximum value) of the output if histeq=TRUE
maxcell	positive integer. The size of the regular sample used to compute the histogram
filename	character. Output filename
...	additional arguments for writing files as in writeRaster

Value

SpatRaster

Examples

r <- rast(nc=10, nr=10)
values(r) <- rep(1:25, 4)
rs <- stretch(r)
s <- c(r, r*2)
sr <- stretch(s)

terra documentation built on Oct. 13, 2023, 5:08 p.m.