Which of a set of points lie within a polygon defined region
Tests whether each of a set of points lie within a region defined by one or more (possibly nested) polygons. Points count as `inside' if they are interior to an odd number of polygons.
- A two column matrix, the rows of which define the vertices of polygons defining the boundary of a region.
Different polygons should be separated by an
NArow, and the polygons are assumed closed.
- A two column matrix. Each row is a point to test for inclusion in the region defined by
The algorithm works by counting boundary crossings (using compiled C code).
TRUEif the corresponding row of
xis inside the boundary and
library(mgcv) data(columb.polys) bnd <- columb.polys[] plot(bnd,type="n") polygon(bnd) x <- seq(7.9,8.7,length=20) y <- seq(13.7,14.3,length=20) gr <- as.matrix(expand.grid(x,y)) inside <- in.out(bnd,gr) points(gr,col=as.numeric(inside)+1)