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Geographic statistics for sets of cells with the same values

Source: R/zonalGeog.r
zonalGeog.Rd

This function calculates geographic statistics for each set of cells in an integer or factor GRaster. Statistics include:

  • Area

  • Perimeter length

  • "Compact square" statistic: \(4 \sqrt(area) / perimeter)\)

  • "Compact circle" statistic: \(4 * P / ( 2 \sqrt(\pi * A))\) where P is the perimeter length and A the area.

  • fractal dimension: \(2 ( log(P) / log(A + 0.001))\) where P is perimeter length and A is area.

  • The average x- and y-coordinates of each zone.

Usage

# S4 method for class 'GRaster'
zonalGeog(x, unit = "meters")

Arguments

x

A GRaster.

unit

Character: Units of the output. Any of:

  • "meters" (default)

  • "kilometers" or "km"

  • "miles" or "mi"

  • "yards" or "yd"

  • "feet" or "ft": International foot; 1 foot exactly equal to 0.3048 meters

  • "cells": Number or cells

Partial matching is used and case is ignored.

Value

A list of data.frames or a data.tables, one per layer in x. Only layers that are integers or factors have their geographies calculated. Other layers have NULL tables returned.

Examples

if (grassStarted()) {

# Setup
library(terra)

# Example data: Elevation and land cover
madElev <- fastData("madElev")
madForest2000 <- fastData("madForest2000")
madCover <- fastData("madCover")

# Convert to GRasters:
elev <- fast(madElev)
forest2000 <- fast(madForest2000)
cover <- fast(madCover)

# Rename
names(elev) <- "elev"
names(forest2000) <- "forest"

# Geometric statistics for an integer raster zoned by elevation:
fun <-
  "= if (elev <400 & forest == 1, 0, if (elev >=400 & forest == 1, 1, null()))"
forestByElev <- app(c(elev, forest2000), fun = fun)
plot(forestByElev, main = "forest < 400 m & >= 400 m")
zonalGeog(forestByElev)

# Geometric statistics for a categorical raster:
zonalGeog(cover)

}