Generating a polygon around points

Hi Bob,

You probably want to have a look at the package alphahull.

Cheers,

Tsjerk

Your question seems to need an answer to, "How do you find a convex hull
on a sphere?"  Google has many references.

Clint Bowman                    INTERNET:       clint at ecy.wa.gov
Air Quality Modeler             INTERNET:       clint at math.utah.edu
Department of Ecology           VOICE:          (360) 407-6815
PO Box 47600                    FAX:            (360) 407-7534
Olympia, WA 98504-7600

        USPS:           PO Box 47600, Olympia, WA 98504-7600
        Parcels:        300 Desmond Drive, Lacey, WA 98503-1274

On Fri, 15 Aug 2014, Bob O'Hara wrote:

 I've been struggling for half a day on what should be a simple problem...
I have a data frame of lat/long coordinates that describe a region, and I
want to draw a polygon around them so I can use that as a boundary (to be
thrown at INLA, but those details aren't important). The coordinates are
almost on a regular grid: there is some variation in latitude (because
we're on a globe).

If the coordinates were on a regular grid, I could use as.owin() to create
a mask, and go on from there (I have code that will work). But as.owin()
doesn't like unevenly spaced points.

Can anyone suggest a way to sort this out? Preferable without having to
mess around transforming the coordinates.

Bob

--
Bob O'Hara

Biodiversity and Climate Research Centre
Senckenberganlage 25
D-60325 Frankfurt am Main,
Germany

Tel: +49 69 798 40226
Mobile: +49 1515 888 5440
WWW:   http://www.bik-f.de/root/index.php?page_id=219
Blog: http://occamstypewriter.org/boboh/
Journal of Negative Results - EEB: www.jnr-eeb.org

        [[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/
posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Tsjerk A. Wassenaar, Ph.D.

	[[alternative HTML version deleted]]

Generating a polygon around points

Thread (15 messages)