Hello,

I have a distribution dataset for species consisting of xy coordinates at
the 1km resolution, with only presence data. So a simplified example of a
species distribution might be:

y <- rbind(as.integer(rnorm(100,50,20)), as.integer(rnorm(200,100,30)),
as.integer(rnorm(100,180,15)))
x <- rbind(as.integer(rnorm(200,50,20)), as.integer(rnorm(200,100,20)),
as.integer(rnorm(100,200,15)))
plot(y~x)

I would like to create polygons for each species distribution, where if an
island is present (as I have tried to show in the example), it would be a
seperate polygon, and the jagged edges where species distributions meet
coastlines etc are maintained. I have tried functions such as mcp in the
package adehabitat, but this produces a very coarse polygon, which doesn't
provide the detailed distribution edges that I need. Other functions I've
tried require the data already to be in the format where the only xy
coordinates present are the outline of the polygon.

Can anyone please recommend a function I can use here, or suggest a way of
extracting the outline points? I have tried this manually but cannot seem
to write a code that will effectively take account of jagged edges and
islands.

Thanks very much for your help,

Louise.

	[[alternative HTML version deleted]]

