[R-sig-Geo] Find incircle of a polygon

[Roger Bivand]

On Wed, 22 Apr 2009, Etienne Bellemare Racine wrote:

> Hi,
> I'm looking for a way to find the largest circle fitting in an irregular
> polygon. This is not the real definition of an incircle (as it has to be
> tangent to all edges, but it's a more synthetic title).
> Spatstat package has an incircle function, but designed for an owin
> class object. Before trying to adapt the function to my needs, so I can
> input a shapefile, I would be happy to get some advices (if any
> available), or another package to look at.

You can read (polygon) shapefiles into SpatialPolygon* objects using 
readShapeSpatial in maptools and readOGR in rgdal. Once there, coerce to 
an owin object with methods in maptools, something like:

x <- readOGR(".", "myshape")
ox <- as(as(x, "SpatialPolygons"), "owin")

should do it, but watch for topology checking in spatstat. Spatstat ships 
with a vignette on using shapefiles, see for an online link:

http://cran.r-project.org/web/packages/spatstat/vignettes/shapefiles.pdf

which is up to date, humourous, and should tell you what you need to know. 
Using the advice there should resolve any topology problems. If you are 
stuck after trying things from there, please follow up on this list.

Hope this helps,

Roger

>
> Thanks,
> Etienne
>
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>
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no