Hi,
I have mapped structures with a GPS (walked along their edges) and Im
now trying to make polygons from my coordinates. The GPS data are a bit
fuzzy and I want to establish the edge of the structure with a smoother
or similar. However, I have not been able to find an easy way to do this
in R. This seems odd to me and I might have missed something. I have so
far tried doing lines with spline (xspline) or polygons with the
alphahull package, but they are tricky to work with (usually overfit).
Any pointers are welcome.
Gustaf
Example code, testing the alphahull package:
require(alphahull)
set.seed(1)
xx <-c(1:10,8,5,2)
xx <- xx + rnorm(39,0,0.4)
yy <-c(1:5,5:1,1,1,1)
yy <-yy + rnorm(39,0,0.4)
plot( xx ~ yy)
xy <-data.frame("x" = xx, "y" = yy)
coords <- coordinates(xy)
# alpha-shape
x.as <- ashape(coords, alpha=5)
# alpha-hull
x.ah <- ahull(coords, alpha=5)
#plot
plot(x.as)
plot(x.ah)
--
Gustaf Granath (PhD)
Post doc
McMaster University
Email: gustaf.gran...@gmail.com
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