[R] Points inside a polygon
Rolf Turner
rolf.turner at xtra.co.nz
Thu Jan 12 20:58:44 CET 2012
On 12/01/12 17:28, Hasan Diwan wrote:
> I have a list of bounds for a series of polygons. I do understand the
> formula to determine whether point i is within polygon X (X[x1]< i[x]
> & X[x2]> i[x]& X[y1]< i[y]& X[y2]> i[y]), and I can apply this
> throughout the dataset. However, this naive algorithm doesn't scale
> very well. The data set contains 10,000 points consisting of (n,e)
> pairs where I'm interested in which are inside polygons denoted by
> vertices (V[x1]/V[y1],V[x2],V[y2]). Is there a shortcut to accomplish
> this goal? Many thanks! --
You could use the function inside.owin() in the "spatstat" package
(after appropriately reconfiguring your polygons as objects of class
"owin"; something like w <- owin(poly=plygn) where "plygn" is your
polygon).
You could also use the undocumented function inside.xypolygon().
cheers,
Rolf Turner
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