[R-sig-Geo] How to get the code of function .spFindCG in package sp?

[Roger Bivand]

On Wed, 8 Nov 2006, Wang, Hao wrote:

> Hi,
> 
> How to dig out the code of the function of .spFindCG, which is used in the function
> Polygon. 

It isn't exported from the sp namespace, so you need to access it within 
the namespace:

sp:::.spFindCG

> 
> I also wanna to know how to calculate the area of a polygon, 

See sp:::.spFindCG and the C source of the function it calls.

> and how could I know if there are intersections of boundary in a
> polygon?

There are no polygon clipping functions in sp. There are some in gpclib 
and PBSmapping; the first of these are used in some wrapper functions 
currently in the sourceforge repository spgpc package, soon to be released 
on CRAN in maptools. Neither of these provide exactly what you need, but 
some of the pieces may be there.

> 
> 
> Best regards,
> 
> Hao
> 
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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