gis - Calculating the distance between polygon and point in R

Question

I have a, not necessarily convex, polygon without intersections and a point outside this polygon. I'm wondering how calculate the Euclidian distance most efficiently in a 2-dimensional space. Is there a standard method in R?

My first idea was to calculate the minimum distance of all the lines of the polygon (extended infinitely so they are line, not line pieces) and then calculate the distance from the point to each individual line using the start of the line piece and Pythagoras.

Do you know about a package that implements an efficient algorithm?

Answer 1

You could use the rgeos package and the gDistance method. This will require you to prepare your geometries, creating spgeom objects from the data you have (I assume it is a data.frame or something similar). The rgeos documentation is very detailed (see the PDF manual of the package from the CRAN page), this is one relevant example from the gDistance documentation:

pt1 = readWKT("POINT(0.5 0.5)")
pt2 = readWKT("POINT(2 2)")
p1 = readWKT("POLYGON((0 0,1 0,1 1,0 1,0 0))")
p2 = readWKT("POLYGON((2 0,3 1,4 0,2 0))")
gDistance(pt1,pt2)
gDistance(p1,pt1)
gDistance(p1,pt2)
gDistance(p1,p2)

readWKT is included in rgeos as well.

Rgeos is based on the GEOS library, one of the de facto standards in geometric computing. If you don't feel like reinventing the wheel, this is a good way to go.