pointsInPolygon: Points Inside Polygon

In secr: Spatially Explicit Capture-Recapture

Points Inside Polygon

Description

Determines which of a set of points lie inside a closed polygon or at least one of a set of polygons

Usage

pointsInPolygon(xy, poly, logical = TRUE)

Arguments

xy	2-column matrix or dataframe of x-y coordinates for points to assess
poly	2-column matrix or dataframe containing perimeter points of polygon, or a SpatialPolygonsDataFrame object from package sp, or a ‘mask’ object (see Warning)
logical	logical to control the output when ‘poly’ is a mask (see Details)

Details

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).

Value

Vector of logical or integer values, one for each row in xy

Warning

If poly is a mask object then its cells must be aligned to the x- and y- axes

See Also

over

Examples

## 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)

secr documentation built on Nov. 4, 2024, 9:06 a.m.