buffer function

Compute Buffers Regions

buffer computes buffers regions from spatial objects belonging to the following classes:

SpatialPoints (all pixels located within a specified distance of a point take the value one)

SpatialPointsDataFrame with one column (this column is considered to be a factor, and the buffer is computed for each level of this factor)

SpatialLines to compute buffers from lines.

SpatialPolygons to compute buffers from polygons.

buffer(xy, x, dist)

Arguments

• xy: an object of class SpatialPoints, SpatialPointsDataFrame with one column (a factor considered to be the identity of the points), SpatialLines, or SpatialPolygons.
• x: an object inheriting the class SpatialPixels with the same attributes (resolution, size) as those desired for the output.
• dist: a value of distance

Returns

An object of class SpatialPixelsDataFrame.

Author(s)

Clement Calenge clement.calenge@ofb.gouv.fr

See Also

SpatialPixelsDataFrame-class for additionnal information on objects of class SpatialPixelsDataFrame.

Examples

data(lynxjura)

# locs is the SpatialPointsDataFrame containing the
# locations of lynx indices in the Jura mountains
locs <- lynxjura$locs
head(locs)

## just for the sake of illustration: sample 100 points
suppressWarnings(RNGversion("3.5.0"))
set.seed(233)
locs <- locs[sample(1:nrow(locs), 100),]

# sa is the SpatialPixelsDataFrame object containing
# maps of the study area
sa <- lynxjura$map

# Buffer of 2000 m from all points
bu <- buffer(locs, sa, 2000)
image(bu)

# displays all the pixels of the study area within 2000 m
# of a point, for each type of indices (see ?lynxjura)
buani <- buffer(locs[,2], sa, 2000)
buani
par(mar=c(0,0,2,0))
opar<-par(mfrow=c(3,4))
lapply(1:11, function(i) {
   image(buani[,i])
   title(main = names(slot(buani, "data"))[i])
})
par(opar)

## buffer from a polygon
sa2 <- sa[,4]
sa2[[1]][sa2[[1]]<5000] <- NA
image(sa2)

## gets the contour line
gc <- getcontour(sa2)
plot(gc, add=TRUE)

## a buffer of 2000 metres
image(buffer(gc, sa, 2000))
plot(gc, add=TRUE)