R help - Aug 2012 - Identify points that lie within polygon

I have a complex 2D polygon with thousands of vertices, and I'd like to be
able to identify points from a large set contained within the polygon, and
was wondering if there might be an efficient way of doing this?  Any advice
would be useful!  Here is a small example of what I mean:

# make polygon
v1<-c(0,1,1,2,1,3,6,7)
v2<-c(1,3,3,5,6,7,8,9)
plot(v1, v2, type = "n" )
polygon(v1, v2, lwd = 2, col = "red")

# plot a set of candidate grid points
grid<-seq(0, 10, length.out = 30)
pts<-expand.grid(grid, grid)
points(pts, pch = 19, col = 1, cex = 1)

Many thanks!

Alastair




--
View this message in context:
http://r.789695.n4.nabble.com/Identify-points-that-lie-within-polygon-tp4639289.html
Sent from the R help mailing list archive at Nabble.com.

Hello,

With your example run and click 10 black points inside the area.

ploc <- locator(n=10)
points(ploc$x, ploc$y, pch = 19, col = "green", cex = 1)

Hope this helps,

Rui Barradas

Em 06-08-2012 16:05, Ally escreveu:
> I have a complex 2D polygon with thousands of vertices, and I'd like to
be
> able to identify points from a large set contained within the polygon, and
> was wondering if there might be an efficient way of doing this?  Any advice
> would be useful!  Here is a small example of what I mean:
>
> # make polygon
> v1<-c(0,1,1,2,1,3,6,7)
> v2<-c(1,3,3,5,6,7,8,9)
> plot(v1, v2, type = "n" )
> polygon(v1, v2, lwd = 2, col = "red")
>
> # plot a set of candidate grid points
> grid<-seq(0, 10, length.out = 30)
> pts<-expand.grid(grid, grid)
> points(pts, pch = 19, col = 1, cex = 1)
>
> Many thanks!
>
> Alastair
>
>
>
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/Identify-points-that-lie-within-polygon-tp4639289.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

This is off-topic (not about R), and a quick Web search of "test within
polygon" yields many results, and adding "R" to the search when
using Google provides hints about applying the algorithms in R.
---------------------------------------------------------------------------
Jeff Newmiller                        The     .....       .....  Go Live...
DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live
Go...
                                      Live:   OO#.. Dead: OO#..  Playing
Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
/Software/Embedded Controllers)               .OO#.       .OO#.  rocks...1k
--------------------------------------------------------------------------- 
Sent from my phone. Please excuse my brevity.

Ally <a.rushworth at stats.gla.ac.uk> wrote:
>I have a complex 2D polygon with thousands of vertices, and I'd like to
>be
>able to identify points from a large set contained within the polygon,
>and
>was wondering if there might be an efficient way of doing this?  Any
>advice
>would be useful!  Here is a small example of what I mean:
>
># make polygon
>v1<-c(0,1,1,2,1,3,6,7)
>v2<-c(1,3,3,5,6,7,8,9)
>plot(v1, v2, type = "n" )
>polygon(v1, v2, lwd = 2, col = "red")
>
># plot a set of candidate grid points
>grid<-seq(0, 10, length.out = 30)
>pts<-expand.grid(grid, grid)
>points(pts, pch = 19, col = 1, cex = 1)
>
>Many thanks!
>
>Alastair
>
>
>
>
>--
>View this message in context:
>http://r.789695.n4.nabble.com/Identify-points-that-lie-within-polygon-tp4639289.html
>Sent from the R help mailing list archive at Nabble.com.
>
>______________________________________________
>R-help at r-project.org mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.