crop: Remove parts of a GRaster or GVector

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

Remove parts of a GRaster or GVector

Description

crop() removes parts of a GRaster or GVector that fall "outside" another raster or vector. You cannot make the GRaster or GVector larger than it already is (see extend()). Rasters may not be cropped to the exact extent, as the extent will be enlarged to encompass an integer number of cells. If you wish to remove certain cells of a raster, see mask().

Usage

## S4 method for signature 'GRaster'
crop(x, y, fail = TRUE)

## S4 method for signature 'GVector'
crop(x, y, extent = FALSE, fail = TRUE)

Arguments

x	A GRaster or GVector to be cropped.
y	A GRaster or GVector to serve as a template for cropping.
fail	Logical: If TRUE (default), and the cropped object would have zero extent in at least one dimension, then exit the function with an error. If FALSE, then display a warning and return NULL.
extent	Logical: If y is a "points" GVector: Use the convex hull around y to crop x. If y is a "lines" or "polygons" GVector: If TRUE, use the extent of y to crop x. if y is a GVector, x will be cropped to the extent of y (extent is ignored).

Details

Known differences from terra::crop():

• If x and y are "points" vectors, and extent is TRUE, terra removes points that fall on the extent boundary. fasterRaster does not remove points on the extent boundary.

• If x is a "points" vector and y is a "lines" vectors, and extent is FALSE, terra uses the extent of y to crop the points. fasterRaster uses the minimum convex hull of the lines vector.

Value

A GRaster or GVector (or NULL if fail is FALSE and the output would have a zero east-west and/or north-south extent).

See Also

terra::crop(), sf::st_crop()

Examples

if (grassStarted()) {

# Setup
library(sf)
library(terra)

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

# Plant specimen points vector
madDypsis <- fastData("madDypsis")

# Rivers lines vector
madRivers <- fastData("madRivers")

# Polygons vector
madCoast4 <- fastData("madCoast4")
madAnt <- madCoast4[madCoast4$NAME_4 == "Antanambe", ]

# Convert to fasterRaster format:
elev <- fast(madElev)
dypsis <- fast(madDypsis)
rivers <- fast(madRivers)
coast <- fast(madCoast4)
ant <- fast(madAnt)

### Crop raster by vector:
rastByVect <- crop(elev, ant)
plot(elev, col = "gray", legend = FALSE)
plot(rastByVect, add = TRUE)
plot(ant, add = TRUE)

### Crop raster by raster:

# For this example, make the SpatRaster smaller, then crop by this.
templateRast <- crop(madElev, madAnt)

template <- fast(templateRast)
rastByRast <- crop(elev, template)

plot(elev, col = "gray", legend = FALSE)
plot(rastByRast, add = TRUE)

### Crop vector by raster:

# For this example, make the SpatRaster smaller, then crop by this.
templateRast <- crop(madElev, madAnt)

template <- fast(templateRast)
ptsByRast <- crop(dypsis, template)

plot(elev, col = "gray", legend = FALSE)
plot(templateRast, add = TRUE)
plot(dypsis, add = TRUE)
plot(ptsByRast, pch = 21, bg = "red", add = TRUE)

### Crop vector by vector:
ptsSubset <- dypsis[1:10] # use first 10 points as cropping template

# Crop points vector by convex hull around points:
ptsByPts <- crop(dypsis, ptsSubset)
plot(dypsis)
plot(convHull(ptsSubset), lty = "dotted", border = "blue", add = TRUE)
plot(ptsByPts, col = "red", add = TRUE)
plot(ptsSubset, col = "blue", pch = 3, cex = 1.6, add = TRUE)
legend("topleft",
    legend = c("Dypsis", "Selected", "Crop template", "Convex hull"),
    pch = c(16, 16, 3, NA),
    lwd = c(NA, NA, NA, 1),
    col = c("black", "red", "blue", "blue"),
    lty = c(NA, NA, NA, "dotted"),
    xpd = NA,
    bg = "white"
)

# Crop points vector by extent of points:
ptsByPts <- crop(dypsis, ptsSubset, ext = TRUE)
plot(dypsis)
plot(ptsByPts, col = "red", add = TRUE)
plot(ptsSubset, col = "blue", pch = 3, cex = 1.6, add = TRUE)
legend("topleft",
    legend = c("Dypsis", "Selected", "Crop template"),
    pch = c(16, 16, 3),
    lwd = c(NA, NA, NA),
    col = c("black", "red", "blue"),
    lty = c(NA, NA, NA),
    xpd = NA,
    bg = "white"
)

# Crop points vector by convex hull around lines:
ptsByPts <- crop(dypsis, rivers)
plot(rivers, col = "blue", pch = 3, cex = 1.6)
plot(dypsis, add = TRUE)
plot(convHull(rivers), lty = "dotted", border = "blue", add = TRUE)
plot(ptsByPts, col = "red", add = TRUE)
legend("topleft",
    legend = c("Dypsis", "Selected", "Rivers", "Convex hull"),
    pch = c(16, 16, NA, NA),
    lwd = c(NA, NA, 1, 1),
    col = c("black", "red", "blue", "blue"),
    lty = c(NA, NA, "solid", "dotted"),
    xpd = NA,
    bg = "white"
)

# Crop points vector by extent of lines:
ptsByPts <- crop(dypsis, rivers, ext = TRUE)
plot(rivers, col = "blue", pch = 3, cex = 1.6)
plot(dypsis, add = TRUE)
plot(convHull(rivers), lty = "dotted", border = "blue", add = TRUE)
plot(ptsByPts, col = "red", add = TRUE)
legend("topleft",
    legend = c("Dypsis", "Selected", "Rivers"),
    pch = c(16, 16, NA),
    lwd = c(NA, NA, 1),
    col = c("black", "red", "blue"),
    lty = c(NA, NA, "solid"),
    xpd = NA,
    bg = "white"
)

# Crop points vector by polygon:
ptsByPts <- crop(dypsis, ant)
plot(dypsis)
plot(ant, border = "blue", pch = 3, cex = 1.6, add = TRUE)
plot(ptsByPts, col = "red", add = TRUE)
legend("topleft",
    legend = c("Dypsis", "Selected", "Antanambe"),
    pch = c(16, 16, NA),
    lwd = c(NA, NA, 1),
    col = c("black", "red", "blue"),
    lty = c(NA, NA, "solid"),
    xpd = NA,
    bg = "white"
)

# Crop lines vector by polygon:
linesByPoly <- crop(rivers, ant)
plot(rivers)
plot(ant, border = "blue", pch = 3, cex = 1.6, add = TRUE)
plot(linesByPoly, col = "red", add = TRUE)
legend("topleft",
    legend = c("Rivers", "Selected", "Antanambe"),
    col = c("black", "red", "blue"),
    lwd = 1,
    xpd = NA,
    bg = "white"
)

# Crop polygon vector by convex hull around points:
polyByPoints <- crop(ant, dypsis)
plot(dypsis, col = "red")
plot(ant, border = "blue", add = TRUE)
plot(polyByPoints, border = "red", add = TRUE)
legend("topleft",
    legend = c("Dypsis", "Antanambe", "Selected"),
    col = c("red", "blue", "red"),
    pch = c(16, NA, NA),
    lwd = c(NA, 1, 1),
    xpd = NA,
    bg = "white"
)

}

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