[R-sig-Geo] External "Envelope" of a set of points in space - not convex hull

[Michael Sumner]

Can you share what you've tried? A triangulation is really at odds
with the representation available with "polygons" in their usual GIS
form, but there are ways to do it. The basic options (to me) are
either a set of the triangles as individual polygons, or even a set of
shapes in a "multipolygon", or to dissolve them to get the hull/s from
the alphahull code. Any feeling for which option is more important?
Got an example of running the alphahull to help someone start, and why
you want a SpatialPolygonsDataFrame? (For plot, export, both, or
other?).



On Wed, Jun 27, 2012 at 6:31 PM, Mathieu Rajerison
<mathieu.rajerison at gmail.com> wrote:
> Hi,
>
> alphahull is nice but having a SpatialPolygonsDataFrame from the result is
> quite tricky
>
> If anyone has the solution..
>
>
> 2012/6/22 Michael Sumner <mdsumner at gmail.com>
>>
>> Try the alphahull package, which is on CRAN.
>>
>> I don't believe it will smooth the result for you, but you could take
>> it from there and use other R functions to do that.
>>
>> Cheers, Mike.
>>
>>
>> On Fri, Jun 22, 2012 at 4:56 PM, PCB <pedrocontebarros at gmail.com> wrote:
>> > Dear All,
>> >
>> > I have a set of observations on an area, and I would like to define the
>> > "investigated area" as the smallest polygon (preferably smoothed with
>> > e.g.
>> > splines fit) that encloses all the points. This is similar to the convex
>> > hull problem, except that my data have "gulfs", i.e. areas that are not
>> > sampled (and should not be), between two "fingers" of areas
>> > investigated. I
>> > am sure I have seen something about solving this lately, but after a
>> > couple
>> > days searching could not find it (I am sure I am using the wrong
>> > keywords...).
>> >
>> > Any help would be appreciated
>> >
>> > --
>> > View this message in context:
>> > http://r-sig-geo.2731867.n2.nabble.com/External-Envelope-of-a-set-of-points-in-space-not-convex-hull-tp7580290.html
>> > Sent from the R-sig-geo mailing list archive at Nabble.com.
>> >
>> > _______________________________________________
>> > R-sig-Geo mailing list
>> > R-sig-Geo at r-project.org
>> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>
>>
>>
>> --
>> Michael Sumner
>> Hobart, Australia
>> e-mail: mdsumner at gmail.com
>>
>> _______________________________________________
>> R-sig-Geo mailing list
>> R-sig-Geo at r-project.org
>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>
>



-- 
Michael Sumner
Hobart, Australia
e-mail: mdsumner at gmail.com