[R] Generating a polygon around points

Tsjerk Wassenaar tsjerkw at gmail.com
Fri Aug 15 17:31:45 CEST 2014


Hi Bob,

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

Cheers,

Tsjerk


On Fri, Aug 15, 2014 at 5:25 PM, Clint Bowman <clint at ecy.wa.gov> wrote:

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



-- 
Tsjerk A. Wassenaar, Ph.D.

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