[R-sig-Geo] minimun distance between polygons' edges

[Mihai Valcu]

You could approach it as a minimum distance between points problem.
With sp,  first convert each SpatialPolygons to SpatialLines,  generate 
regular points on each line and then compute minimum dist between all 
points. Obviously, there is a trade off  between the number of points 
and precision.

Something like this:

require(sp)

# 1st  "polygon"
p1 = SpatialLines(list(Lines(list(Line(cbind(c(10.92, 8.13, 17.12, 
29.97, 31.06, 25.95, 20.21,10.92),
c(86.56, 73.24, 59.75, 67.54, 75.84, 86.39, 95.04,86.56) ))))))

# 2nd "polygon"
p2 = SpatialLines(list(Lines(list(Line(cbind(c(41.75, 35.55, 42.68, 
53.99, 60.96, 58.94, 53.21,41.75),
c(66.5, 53.87, 41.07, 42.11, 51.62, 64.77, 67.36,66.5)))))))

plot(1:100, type = "n")
plot(p1, add = T)
plot(p2, add = T)


# regular  sampling on each polygon
n = 500
p1.pts = spsample(p1, n = n, type = "regular")
p2.pts = spsample(p2, n = n, type = "regular")

# minimun distance between polygons' edges
min(apply(coordinates(p1.pts), 1, function(p) 
spDistsN1(coordinates(p2.pts), p )))


...
Mihai





Marion TAFANI wrote:
> dear all,
>
> we want to calculate the minimun distance between polygons' edges , do 
> you know any package or function which can help us ? we try to work 
> with vectors rather than raster but we lack some tools. we only found 
> how to calculate distances between centroids but nothing between edges.
>
> thanks
>
>
>
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