is.insidePolygon {tigers}

Test If a Point Is Inside a Polygon

Description

This function tests if a point is inside a polygon.

Usage

is.insidePolygon(XY, points)

Arguments

XY

A two-column matrix giving the coordinates of a polygon.

points

a vector with two values giving the coordinates of a point, or a matrix with two columns.

Details

The algorithm is based on “ray-tracing”: a segment is traced between points and an arbitrary point far from the polygon. If this segment intersects an odd number of edges of the polygon, then points is inside the polygon.

The polygon must be open and can be in either clockwise or counterclockwise order. If the polygon is closed, it is modified internally without warning (the original polygon is not modified).

Value

a logical vector indicating whether each point is inside the polygon defined by XY.

Author(s)

Emmanuel Paradis

See Also

is.open

Examples

XY <- rbind(c(0, 0), c(0, 1), c(1, 1), c(1, 0))
stopifnot(is.insidePolygon(XY, c(0.5, 0.5)))
stopifnot(!is.insidePolygon(XY, c(1.5, 1.5)))