I'd like to create a a .shp file or data table of coordinates where the output point features are where line endpoints touch at a point on the polygon boundary and where lines cross polygon boundaries. No points are generated in the output where lines lie directly along polygon boundaries.
Can this be done in R?
Like the intersect tool in Esri?
I have both classes (in R)...
I simply can't seem to find a tool/package that does this...
(I am a beginner)
You can do this with the spatstat package, but you need to convert
from SpatialLines and SpatialPolygons to psp (planar segment
pattern) and owin (observation window -- a polygon in the plane) using
the maptools package.
Since you didn't provide example data I will first construct SpatialPolygons and SpatialLines objects looking like your graphic:
library(maptools)
#> Loading required package: sp
#> Checking rgeos availability: TRUE
library(spatstat)
#> Loading required package: nlme
#> Loading required package: rpart
#>
#> spatstat 1.48-0.029 (nickname: 'Alternative Facts')
#> For an introduction to spatstat, type 'beginner'
A <- owin(c(1,3), c(2,5))
B <- owin(c(4,7), c(1,5))
p <- union.owin(A,B)
p <- as(p, "SpatialPolygons")
l <- psp(c(0.5, 0.5), c(2, 4), c(4, 6), c(2, 4), window = owin(c(0,7), c(0,5)))
l <- as(l, "SpatialLines")
plot(p)
plot(l, col = "green", add = TRUE, lwd = 3)
Now to do what you ask you convert the edges of the polygon to a psp
and find where the lines cross these edges (returned as a planar point
pattern ppp):
l <- as(l, "psp")
p <- as(p, "owin")
e <- edges(p)
x <- crossing.psp(l, e)
x
#> Planar point pattern: 4 points
#> window: rectangle = [1, 6] x [2, 4] units
Adding the points to the plots shows what we found:
plot(p, main = "")
plot(l, col = "green", add = TRUE, lwd = 3)
plot(x, add = TRUE, col = "red", pch = 20, cex = 3)
