tiles: Divide a GRaster into spatially exclusive subsets

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

Divide a GRaster into spatially exclusive subsets

Description

This function divides a GRaster into "tiles" or spatial subsets which can be used for speeding some raster calculations. Tiles can be mutually exclusive or overlap by a user-defined number of cells.

Usage

## S4 method for signature 'GRaster'
tiles(x, n, overlap = 0, verbose = FALSE)

Arguments

x	A GRaster with one or more layers.
n	Numeric vector: Number of tiles to create. This can be a single number, in which case x is divided into n × n tiles, or two values in which case it is divided into n[1] × n[2] tiles (rows x columns).
overlap	Numeric vector (default is 0): Number of rows/columns by which to expand the size of tiles so they overlap. This can be a single value or two values. If just one is provided, the tiles will be expanded by overlap rows and overlaps columns. If two numbers are provided, the tiles will be expanded by overlap[1] rows and overlap[2] columns.
verbose	Logical: If TRUE, display progress. Default is FALSE. Progress is only displayed if x is a multi-layer GRaster.

Value

If x has just one layer, then the output is a list with one element per tile. The lapply() and sapply() functions can be used to apply functions to each tile in the list. If x has more than one layer, then the output will be a list of lists, with each sub-list containing the tiles for one GRaster layer.

Examples

if (grassStarted()) {

# Setup
library(terra)

# Elevation raster
madElev <- fastData("madElev")

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

# Create spatially exclusive tiles:
exclusive <- tiles(elev, n = 2, verbose = TRUE)

startpar <- par(mfrow = c(2, 3))
plot(elev, main = "Original")

for (i in seq_along(exclusive)) {
	plot(exclusive[[i]], ext = elev, main = paste("Tile", i))
}
par(startpar)

# Create tiles that overlap:
overlaps <- tiles(elev, n = 2, overlap = 200, verbose = TRUE)

startpar <- par(mfrow = c(2, 3))
plot(elev, main = "Original")

for (i in seq_along(overlaps)) {
	plot(overlaps[[i]], ext = elev, main = paste("Tile", i))
}
par(startpar)

}

adamlilith/fasterRaster documentation built on Dec. 21, 2024, 2:04 a.m.