For a series of points and a set of SpatialPolygons that are irregularly shaped, how do I detect which of the points sit inside which Polygon?

Question

If I have a set of SpatialPolygons created as such:

library(sp)

Sr2 = Polygon(cbind(c(2,2,1,2,4,4,2),c(2,6,7,7,5,3,2)))
Sr3 = Polygon(cbind(c(4,4,2,5,10,4),c(5,3,2,2,5,5)))
Sr4 = Polygon(cbind(c(5,6,6,5,5),c(4,4,3,3,4)), hole = TRUE)

Srs2 = Polygons(list(Sr2), "s2")
Srs3 = Polygons(list(Sr3, Sr4), "s3/4")
SpP = SpatialPolygons(list(Srs2, Srs3), 1:2)
plot(SpP, col = 2:3, pbg = "white")

Such that it looks like this:

And a vector of points created by:

x <- c(2, 1, 3, 4, 2, 2)
y <- c(2, 4, 2, 2, 3, 4)
points <- cbind(x, y)

How can I detect which points sit inside which polygon, if either?

Thanks

OP is trying to find which point is inside which polygon. Would you say this is sufficiently different to the proposed duplicate, @Pascal? — Roman Luštrik, Mar 11 '15 at 09:33
@Pascal, I'm poking around to see if this is indeed a question worthy of my close vote due to duplication. As I currently see it it's marginal, hence my inquiry. — Roman Luštrik, Mar 11 '15 at 10:06
@RomanLuštrik Sorry for misunderstanding your comment. Maybe not a duplicate, yes. I should have point this question out, as possible help. — , Mar 11 '15 at 10:15
Thank you both for your responses, Pascal my question is indeed a duplicate of that one. I apologise for doubling up and appreciate your pointing me in the right direction and hence answering my question. — Eugene Brown, Mar 18 '15 at 02:36

score 3 · Answer 1 · answered Mar 11 '15 at 07:50

3

You can use over():

over(SpatialPoints(points), SpP)
# 1  2  3  4  5  6 
# 2 NA  2  2  1  1 

plot(SpP, col = 2:3, pbg = "white", axes=TRUE)
plot(SpatialPoints(points), pch=as.character(1:6), add=TRUE)

plot

answered Mar 11 '15 at 07:50

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score 1 · Answer 2 · answered Mar 12 '15 at 07:20

In addition to over you could also use functions from rgeos:

library(rgeos)
pts1 <- gIntersection(SpatialPoints(points), SpP)
plot(SpP, col = 2:3, pbg = "white", axes=TRUE)
points(pts1, pch = 20, col = "blue")

enter image description here

If you want to know the intersection for each point and/or polygon you can use:

gIntersects(SpatialPoints(points), SpP, byid = TRUE)
##        1     2     3     4     5     6
## s2   TRUE FALSE FALSE FALSE  TRUE  TRUE
## s3/4 TRUE FALSE  TRUE  TRUE FALSE FALSE

If the polygon doesn't mapper you could use either:

apply(gIntersects(SpatialPoints(points), SpP, byid = TRUE), 2, any)
##     1     2     3     4     5     6 
##  TRUE FALSE  TRUE  TRUE  TRUE  TRUE

or

gIntersects(SpatialPoints(points), gUnaryUnion(SpP), byid = TRUE)
##      1     2    3    4    5    6
## 1 TRUE FALSE TRUE TRUE TRUE TRUE

For a series of points and a set of SpatialPolygons that are irregularly shaped, how do I detect which of the points sit inside which Polygon?

2 Answers2