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Geographic distance

Source: R/distance.r
distance.Rd

This function produces a raster or a matrix of geographic distances, depending on the input:

Case 1: Argument x is a GRaster and y is missing: By default, this function replaces values in all NA cells with the distance between them and their closest non-NA cell. Alternatively, all non-NA cells can have their values replaced by the distance to NA cells. You can also specify which cells (by value) have their values replaced by distance to other cells.

Case 2: Argument x is a GRaster and y is a GVector: All cells in the raster have their value replaced by the distance to the nearest features in the GVector. Alternatively, calculate the distance from any cell covered by a vector object and the nearest cell not covered by a vector object. Note that the vector is rasterized first.

Case 3: Argument x is a GVector and y is a GVector: A matrix of pairwise distances between all features in one versus the other GVector is returned.

Case 4: Argument x is a GVector and y is missing: A matrix of pairwise distances between all features in the GVector is returned.

Usage

# S4 method for class 'GRaster,missing'
distance(
  x,
  y,
  target = NA,
  fillNA = TRUE,
  unit = "meters",
  method = ifelse(is.lonlat(x), "geodesic", "Euclidean"),
  minDist = NULL,
  maxDist = NULL
)

# S4 method for class 'GRaster,GVector'
distance(
  x,
  y,
  fillNA = TRUE,
  thick = TRUE,
  unit = "meters",
  method = ifelse(is.lonlat(x), "geodesic", "Euclidean"),
  minDist = NULL,
  maxDist = NULL
)

# S4 method for class 'GVector,GVector'
distance(x, y, unit = "meters", minDist = NULL, maxDist = NULL)

# S4 method for class 'GVector,missing'
distance(x, y, unit = "meters", minDist = NULL, maxDist = NULL)

Arguments

x

A GRaster or GVector.

y

Either missing, or a GVector.

target

Numeric: Only applicable for case 1, when x is a GRaster and y is missing. If this is NA (default), then cells with NAs have their values replaced with the distance to the nearest non-NA cell. If this is another value, then cells with these values have their values replaced with the distance to any other cell (meaning, both NA and non-NA, except for cells with this value).

fillNA

Logical: Determines which raster cells to fill with distances.

  • Case 1, when x is a GRaster and y is missing: If TRUE (default), fill values of NA cells with distances to non-NA cells. If FALSE, fill non-NA cells width distance to NA cells.

  • Case 2, when x is a GRaster and y is a GVector: If TRUE (default), then the returned raster will contain the distance from the cell to the closest feature in the vector. If FALSE, then cells covered by the vector will have their values replaced with the distance to the nearest cell not covered, and cells that are not covered by the vector will have values of 0.

  • Case 3, when x is a GVector and y is a GVector: This argument is not used in this case.

unit

Character: Units of the output. Any of:

  • "meters", "metres", or "m" (default)

  • "kilometers" or "km"

  • "miles" or "mi"

  • "nautical miles" or "nmi"

  • "yards" or "yd"

  • "feet" or "ft" – international, 1 foot exactly equals 0.3048 meters

Partial matching is used and case is ignored.

method

Character: The type of distance to calculate. Partial matching is used and capitalization is ignored. Possible values include:

  • Euclidean (default for projected rasters): Euclidean distance.

  • geodesic (default for unprojected rasters): Geographic distance. If x is unprojected (e.g., WGS84 or NAD83), then the method must be "geodesic".

  • squared: Squared Euclidean distance (faster than just Euclidean distance but same rank–good for cases where only order matters).

  • maximum: Maximum Euclidean distance.

  • Manhattan: Manhattan distance (i.e., "taxicab" distance, distance along cells going only north-south and east-west and never along a diagonal).

minDist, maxDist

Either NULL (default) or numeric values: Ignore distances less than or greater than these distances.

thick

Logical: Only applicable for case 2, when x is a GRaster and y is a GVector. If TRUE (default), then the vector will be represented by "thickened" lines (i.e., any cell that the line/boundary touches, not just the ones on the rendering path).

Value

If x is a GRaster, then the output is a GRaster. If x is a GVector, then the output is a numeric vector.

See also

terra::distance(); GRASS modules r.grow.distance and v.distance

Examples

if (grassStarted()) {

# Setup
library(sf)
library(terra)

# Elevation raster, rivers vector, locations of Dypsis plants
madElev <- fastData("madElev")
madRivers <- fastData("madRivers")
madDypsis <- fastData("madDypsis")

# Convert a SpatRaster to a GRaster, and sf to a GVector
elev <- fast(madElev)
rivers <- fast(madRivers)
dypsis <- fast(madDypsis)

### case 1: GRaster by itself

# Distance between NA cells and nearest non-NA cells
naDist <- distance(elev)
names(naDist) <- "NA Distance"
plot(naDist)

# Distance between non-NA cells and nearest NA cells
nonNaDist <- distance(elev, fillNA = FALSE)
names(nonNaDist) <- "non-NA Distance"
plot(nonNaDist)

# Distance between cells with an elevation of 3 and any other cell that != 3
distFocal3 <- distance(elev, target = 3)
names(distFocal3) <- "Distance from 3"
plot(distFocal3)

# Distance between any cell and cells with a value of 3
distTo3 <- distance(elev, fillNA = FALSE, target = 3)
names(distTo3) <- "Distance to 3"
plot(distTo3)

### Case 2: GRaster and GVector
distToVect <- distance(elev, rivers)

plot(distToVect)
plot(rivers, add = TRUE)

### Case 3: GVector vs GVector
plot(rivers)
plot(dypsis, add = TRUE)

distToRivers <- distance(dypsis, rivers, unit = "yd")
distToPlants <- distance(rivers, dypsis)
distToRivers
distToPlants

### Case 4: GVector vs itself
distToItself <- distance(dypsis)
distToItself

}