Mathematical operations on each layer of a GRasters

You can apply mathematical functions to each layer of a GRaster. The output is a GRaster with the same number or layers as the input. Available functions include:

• NAs:

  • is.na()

  • not.na()

• Absolute value: abs()

• Trigonometric functions (assumes values are in radians):

  • cos()

  • sin()

  • tan()

  • acos()

  • asin()

  • atan()

  • atan2()

• Exponential and logarithmic functions:

  • exp()

  • log() (natural log)

  • ln() (also natural log)

  • log2() (log, base 2)

  • log10() (log, base 10)

  • log1p() (same as log(x + 1))

  • log10p() (same as log(x + 1, base = 10))

• Power functions:

  • sqrt()

  • x^y

• Rounding:

  • round()

  • floor() (round down)

  • ceiling() (round up)

  • trunc() (remove decimal portion)

Usage

# S4 method for class 'GRaster'
is.na(x)

# S4 method for class 'GRaster'
not.na(x, falseNA = FALSE)

# S4 method for class 'GRaster'
abs(x)

# S4 method for class 'GRaster'
sin(x)

# S4 method for class 'GRaster'
cos(x)

# S4 method for class 'GRaster'
tan(x)

# S4 method for class 'GRaster'
asin(x)

# S4 method for class 'GRaster'
acos(x)

# S4 method for class 'GRaster'
atan(x)

# S4 method for class 'GRaster,GRaster'
atan2(y, x)

# S4 method for class 'GRaster'
exp(x)

# S4 method for class 'GRaster'
log1p(x)

# S4 method for class 'GRaster'
log10p(x)

# S4 method for class 'GRaster'
log(x, base = exp(1))

# S4 method for class 'GRaster'
ln(x)

# S4 method for class 'GRaster'
log2(x)

# S4 method for class 'GRaster'
log10(x)

# S4 method for class 'GRaster'
sqrt(x)

# S4 method for class 'GRaster'
round(x, digits = 0)

# S4 method for class 'GRaster'
floor(x)

# S4 method for class 'GRaster'
ceiling(x)

# S4 method for class 'GRaster'
trunc(x)

Arguments

x, y

GRasters.

falseNA

Logical (function not.na()): If FALSE (default), non-NA cells will be converted to 1, and NA cells to 0. If TRUE, non-NA cells will be converted to and NA cells will stay as NA.

base

Numeric: Base of the logarithm.

digits

Numeric: Number of digits to round to. If negative, then rounding is to the nearest positive power of 10. For example, if digits = -2, then the GRaster values are rounded to the nearest 100.

Value

A GRaster.

Examples

if (grassStarted()) {

# Setup
library(sf)
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

# do some math
elev + 100
elev - 100
elev * 100
elev / 100
elev ^ 2
elev %/% 100 # divide then round down
elev %% 100 # modulus

100 + elev
100 %/% elev
100 %% elev

elevs + 100
100 + elevs

# math with logicals
elev + TRUE
elev - TRUE
elev * TRUE
elev / TRUE
elev ^ TRUE
elev %/% TRUE # divide then round down
elev %% TRUE # modulus

elevs + TRUE
TRUE + elevs

# Raster interacting with raster(s):
elev + elev
elev - elev
elev * elev
elev / elev
elev ^ log(elev)
elev %/% sqrt(elev) # divide then round down
elev %% sqrt(elev) # modulus

elevs + elev
elev * elevs

# sign
abs(-1 * elev)
abs(elevs)

# powers
sqrt(elevs)

# trigonometry
sin(elev)
cos(elev)
tan(elev)

asin(elev)
acos(elev)
atan(elev)

atan(elevs)
atan2(elev, elev^1.2)
atan2(elevs, elev^1.2)
atan2(elev, elevs^1.2)
atan2(elevs, elevs^1.2)

# logarithms
exp(elev)
log(elev)
ln(elev)
log2(elev)
log1p(elev)
log10(elev)
log10p(elev)
log(elev, 3)

log(elevs)

# rounding
round(elev + 0.5)
floor(elev + 0.5)
ceiling(elev + 0.5)
trunc(elev + 0.5)

# comparison
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

# Mathematical functions on GRasters with >= 2 layers:
mean(elevs)
mmode(elevs)
median(elevs)
nunique(elevs)

sum(elevs)
count(elevs)
min(elevs)
max(elevs)
range(elevs)
skewness(elevs)
kurtosis(elevs)

which.min(elevs)
which.max(elevs)

slope(elevs)
intercept(elevs)
r2(elevs)
tvalue(elevs)

stdev(elevs)
stdev(elevs, pop = FALSE)
var(elevs)
varpop(elevs)

# Note: To get quantiles for each layer, use
# global(x, "quantile", probs = 0.2).
quantile(elevs, 0.1)

}