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Logic-methods operations on GRasters

Source: R/08_logic.r
Logic-methods.Rd

You can do logical operations on GRasters. A cell with a value of 1 is interpreted as TRUE, and a value of 0 is interpreted as FALSE. You can compare:

  • A GRaster to another GRaster

  • A GRaster to a logical value (TRUE or FALSE, but not NA–see not.na())

  • A GRaster to a numeric or integer value that is 0 or 1

Operators include:

  • |: TRUE if either condition is TRUE (or 1), but returns NA if either condition is NA.

  • &: TRUE if both conditions are TRUE (or 1), but NA if either is NA.

Usage

# S4 method for class 'GRaster,GRaster'
Logic(e1, e2)

# S4 method for class 'logical,GRaster'
Logic(e1, e2)

# S4 method for class 'GRaster,logical'
Logic(e1, e2)

# S4 method for class 'GRaster,numeric'
Logic(e1, e2)

# S4 method for class 'numeric,GRaster'
Logic(e1, e2)

# S4 method for class 'GRaster,integer'
Logic(e1, e2)

# S4 method for class 'integer,GRaster'
Logic(e1, e2)

Arguments

e1, e2

Two GRasters, or a GRaster and a logical value (TRUE or FALSE, but not NA), a numeric value that is 0 or 1 (but not NA_real_), or an integer value that is 0 or 1 (but not NA_integer_).

Value

A binary GRaster (1 ==> TRUE, 0 ==> FALSE, plus NA when comparison results in NA).

Examples

if (grassStarted()) {

# Setup
library(terra)

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

# Convert a SpatRaster to a GRaster
elev <- fast(madElev)
elevs <- c(elev, elev, log10(elev) - 1, sqrt(elev))
names(elevs) <- c("elev1", "elev2", "log_elev", "sqrt_elev")

elev
elevs

# Comparisons
elev < 100
elev <= 100
elev == 100
elev != 100
elev > 100
elev >= 100

elev + 100 < 2 * elev

elevs > 10
10 > elevs

# logic
elev < 10 | elev > 200
elev < 10 | cos(elev) > 0.9

elev < 10 | TRUE
TRUE | elev > 200

elev < 10 | FALSE
FALSE | elev > 200

elev < 10 & cos(elev) > 0.9

elev < 10 & TRUE
TRUE & elev > 200

elev < 10 & FALSE
FALSE & elev > 200

}