distance function

Geographic distance

If x is a SpatRaster :

If y is missing this method computes the distance, for all cells that are NA in SpatRaster x to the nearest cell that is not NA (or other values, see arguments "target" and "exclude").

If y is a numeric value, the cells with that value are ignored. That is, distance to or from these cells is not computed (only if grid=FALSE).

If y is a SpatVector, the distance to that SpatVector is computed for all cells, optionally after rasterization.

The distance is always expressed in meter if the coordinate reference system is longitude/latitude, and in map units otherwise. Map units are typically meter, but inspect crs(x) if in doubt.

Results are more precise, sometimes much more precise, when using longitude/latitude rather than a planar coordinate reference system, as these distort distance.

If x is a SpatVector :

If y is missing, a distance matrix between all objects in x is computed. A distance matrix object of class "dist" is returned.

If y is a SpatVector the geographic distance between all objects is computed (and a matrix is returned). If both sets have the same number of points, and pairwise=TRUE, the distance between each pair of objects is computed, and a vector is returned.

If x is a matrix :

x should consist of two columns, the first with "x" (or longitude) and the second with "y" coordinates (or latitude). If y is a also a matrix, the distance between each points in x and all points in y is computed, unless pairwise=TRUE

If y is missing, the distance between each points in x with all other points in x is computed, unless sequential=TRUE

## S4 method for signature 'SpatRaster,missing'
distance(x, y, target=NA, exclude=NULL, unit="m", method="haversine", 
                        maxdist=NA, values=FALSE, filename="", ...)

## S4 method for signature 'SpatRaster,SpatVector'
distance(x, y, unit="m", rasterize=FALSE, method="cosine", filename="", ...)

## S4 method for signature 'SpatVector,ANY'
distance(x, y, sequential=FALSE, pairs=FALSE, symmetrical=TRUE, unit="m", method="geo")

## S4 method for signature 'SpatVector,SpatVector'
distance(x, y, pairwise=FALSE, unit="m", method="cosine")

## S4 method for signature 'matrix,matrix'
distance(x, y, lonlat, pairwise=FALSE, unit="m", method="geo")

## S4 method for signature 'matrix,missing'
distance(x, y, lonlat, sequential=FALSE, pairs=FALSE, symmetrical=TRUE,
                        unit="m", method="geo")

Arguments

• x: SpatRaster, SpatVector, or two-column matrix with coordinates (x,y) or (lon,lat)
• y: missing, numeric, SpatVector, or two-column matrix
• target: numeric. The value of the cells for which distances to cells that are not NA should be computed
• exclude: numeric. The value of the cells that should not be considered for computing distances
• unit: character. Can be either "m" or "km"
• method: character. One of "geo", "cosine" or "haversine" (the latter cannot be used for distances to lines or polygons). With "geo" the most precise but slower method of Karney (2003) is used. The other two methods are faster but less precise
• maxdist: numeric. Distance above this values are not set to NA
• values: logical. If TRUE, the value of the nearest non-target cell is returned instead of the distance to that cell
• rasterize: logical. If TRUE distance is computed from the cells covered by the geometries after rasterization. This can be much faster in some cases
• filename: character. Output filename
• ...: additional arguments for writing files as in writeRaster
• sequential: logical. If TRUE, the distance between sequential geometries is returned
• pairwise: logical. If TRUE and if x and y have the same size (number of rows), the pairwise distances are returned instead of the distances between all elements
• lonlat: logical. If TRUE the coordinates are interpreted as angular (longitude/latitude). If FALSE they are interpreted as planar
• pairs: logical. If TRUE a "from", "to", "distance" matrix is returned
• symmetrical: logical. If TRUE and pairs=TRUE, the distance between a pair is only included once. The distance between geometry 1 and 3 is included, but the (same) distance between 3 and 1 is not

Returns

SpatRaster, numeric, matrix, or a distance matrix (object of class "dist")

Note

A distance matrix can be coerced into a regular matrix with as.matrix

See Also

nearest, nearby

References

Karney, C.F.F., 2013. Algorithms for geodesics, J. Geodesy 87: 43-55. doi:10.1007/s00190-012-0578-z.

Examples

#lonlat
r <- rast(ncols=36, nrows=18, crs="+proj=longlat +datum=WGS84")
r[500] <- 1
d <- distance(r, unit="km") 
plot(d / 1000)

#planar
rr <- rast(ncols=36, nrows=18, crs="+proj=utm +zone=1 +datum=WGS84")
rr[500] <- 1
d <- distance(rr) 

rr[3:10, 3:10] <- 99
e <- distance(rr, exclude=99) 

p1 <- vect(rbind(c(0,0), c(90,30), c(-90,-30)), crs="+proj=longlat +datum=WGS84")
dp <- distance(r, p1) 

d <- distance(p1)
d
as.matrix(d)

p2 <- vect(rbind(c(30,-30), c(25,40), c(-9,-3)), crs="+proj=longlat +datum=WGS84")
dd <- distance(p1, p2)
dd
pd <- distance(p1, p2, pairwise=TRUE)
pd
pd == diag(dd)

# polygons, lines
crs <- "+proj=utm +zone=1"
p1 <- vect("POLYGON ((0 0, 8 0, 8 9, 0 9, 0 0))", crs=crs)
p2 <- vect("POLYGON ((5 6, 15 6, 15 15, 5 15, 5 6))", crs=crs)
p3 <- vect("POLYGON ((2 12, 3 12, 3 13, 2 13, 2 12))", crs=crs)
p <- rbind(p1, p2, p3)
L1 <- vect("LINESTRING(1 11, 4 6, 10 6)", crs=crs)
L2 <- vect("LINESTRING(8 14, 12 10)", crs=crs)
L3 <- vect("LINESTRING(1 8, 12 14)", crs=crs)
lns <- rbind(L1, L2, L3)
pts <- vect(cbind(c(7,10,10), c(3,5,6)), crs=crs)

distance(p1,p3)
distance(p)
distance(p,pts)
distance(p,lns)
distance(pts,lns)