stretch: Rescale values in a raster

In adamlilith/fasterRaster: Faster Raster and Spatial Vector Processing Using 'GRASS GIS'

Rescale values in a raster

Description

stretch() rescales the values in a GRaster. All values can be rescaled, or just values in a user-defined range. This range can be given by specifying either the lower and upper bounds of the range using smin and smax, and/or by the quantiles (across all cells of the raster) using minq and maxq.

Usage

## S4 method for signature 'GRaster'
stretch(x, minv = 0, maxv = 255, minq = 0, maxq = 1, smin = NA, smax = NA)

Arguments

x	A GRaster.
minv, maxv	Numeric: Minimum and maximum values to which to rescale values.
minq, maxq	Numeric: Specifies range of values to rescale, given by their quantiles. The default is to stretch all values (the 0th and 100th quantiles). One or both are ignored if smin and/or smax are provided.
smin, smax	Numeric or NA: Specifies range of values to rescale. If NA (default), then all values are rescaled.

Value

A GRaster.

See Also

terra::stretch() and module r.rescale in GRASS (not used on this function)

Examples

if (grassStarted()) {

# Setup
library(terra)

# Example data
madElev <- fastData("madElev")

# Convert a SpatRaster to a GRaster
elev <- fast(madElev)

### Stretch based on user-defined range
#######################################

#  fasterRaster
fr <- stretch(elev, smin=1, smax=100)
fr

# terra
tr <- stretch(madElev, smin = 1, smax = 100)
tr

# Compare fasterRaster to terra output
fr <- rast(fr)
fr <- extend(fr, tr)
fr - tr

### Stretch values in a certain quantile range
##############################################

#  fasterRaster
fr <- stretch(elev, minq = 0.25, maxq = 0.75)
fr

# terra
tr <- stretch(madElev, minq = 0.25, maxq = 0.75)
tr

# Compare fasterRaster to terra output
fr <- rast(fr)
fr <- extend(fr, tr)
fr - tr

}

adamlilith/fasterRaster documentation built on Sept. 23, 2024, 1:28 a.m.