inpoly: Point in polygon

In kuwisdelu/matter: Scientific computing for out-of-memory signals and images

Point in polygon

Description

Check if a series of x-y points are contained in a closed 2D polygon.

Usage

inpoly(points, poly)

Arguments

points	A 2-column numeric matrix with the points to check.
poly	A 2-column numeric matrix with the vertices of the polygon.

Details

This function works by extending a horizontal ray from each point and counting the number of times it crosses an edge of the polygon.

Value

A logical vector that is TRUE for points that are fully inside the polygon, a vertex, or on an edge, and FALSE for points fully outside the polygon.

Note

There are various public implementations of this function with no clear original source. The version implemented here is loosely based on code by W. Randolph Franklin with modifications so that vertices and points on edges are considered inside the polygon.

Author(s)

W. R. Franklin and Kylie A. Bemis

References

W. R. Franklin. “PNPOLY - Point Inclusion in Polygon Test.” https://wrfranklin.org/Research/Short_Notes/pnpoly.html, 1970.

M. Shimrat, "Algorithm 112, Position of Point Relative to Polygon", Comm. ACM 5(8), pp. 434, Aug 1962.

E. Haines. “Point in Polygon Strategies.” http://www.acm.org/pubs/tog/editors/erich/ptinpoly/, 1994.

See Also

kdsearch

Examples

poly <- data.frame(
        x=c(3,5,5,3),
        y=c(3,3,5,5))
xy <- data.frame(
    x=c(4,6,4,2,3,5,5,3,4,5,4,4,
        3.5,4.5,4.0,3.5),
    y=c(2,4,6,4,3,3,5,5,3,4,5,3,
        4.0,4.0,4.5,4.0),
    ref=c(
        rep("out", 4),
        rep("vertex", 4),
        rep("edge", 4),
        rep("in", 4)))

xy$test <- inpoly(xy[,1:2], poly)
xy

kuwisdelu/matter documentation built on May 1, 2024, 5:17 a.m.