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Determines which of a set of points lie inside a closed polygon or at least one of a set of polygons
pointsInPolygon(xy, poly, logical = TRUE)Vector of logical or integer values, one for each row in xy
2-column matrix or dataframe of x-y coordinates for points to assess
2-column matrix or dataframe containing perimeter points of polygon, or a SpatialPolygonsDataFrame object from package sp, or a `mask' object (see Warning)
logical to control the output when `poly' is a mask (see Details)
If poly is a mask object then its cells must be
aligned to the x- and y- axes
If poly is a SpatialPolygonsDataFrame object then the method
over is used from sp. This allows multiple polygons and
polygons with holes.
If poly is an secr `mask' object then xy is discretized
and matched to the cells in poly. If logical = FALSE
then the returned value is a vector of integer indices to the row in
`poly' corresponding to each row of `xy'; otherwise the result is a
vector of logical values.
Otherwise, the algorithm is adapted from some code posted on the S-news list by Peter Perkins (23/7/1996). The polygon should be closed (last point same as first).
## 100 random points in unit square
xy <- matrix(runif(200), ncol = 2)
## triangle centred on (0.5, 0.5)
poly <- data.frame(x = c(0.2,0.5,0.8,0.2), y = c(0.2,0.8,0.2,0.2))
plot(xy, pch = 1 + pointsInPolygon(xy, poly))
lines(poly)
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