[R-sig-Geo] problem with csr {splancs}

[Roger Bivand]

On Wed, 4 May 2011, António M. Rodrigues wrote:

> Hi,
>
>
> I need to create a number of random points inside a polygon using car
> {splancs}.
>
>
> Let's say I have a SpatialPolygonsDataFrame with only one polygon, and I
> want to throw 100 points inside randomly.
>
>
> If the object is called poly1, I thought this would work:
>
>
>> csr(poly1,100)

?csr perhaps? "poly: A polygon data set", not a SpatialPolygons object. If 
you do:

data(bodmin)
str(bodmin$poly)

you see that splancs, which is effectively unchanged since written almost 
20 years ago, needs a two-column matrix. In your case, if poly1 is a 
SpatialPolygons object with a single Polygons object, which in turn has a 
single member Polygon object, the polygon for splancs would be:

poly1pl <- slot(slot(slot(poly1, "polygons")[[1]], "Polygons")[[1]],
   "coords")

Perhaps we should start planning for a birthday party for splancs, one of 
the real achievements in S/R and spatial statistics!

Roger

>
>
> But I get the error:
>
>
> Error in `[.data.frame`(x at data, i, j, ..., drop = FALSE) :
>
>  undefined columns selected
>
>
> I thought this might have to do with the class, so I did:
>
>
>> teste <- slot(poly1,"polygons")
>
>
> And tried
>
>> csr(teste,100)
>
>
> Now I get:
>
> Error in poly[, 1] : incorrect number of dimensions
>
>
> I apologise if this is a very simple question.
>
> Thanks in advance,
>
> Ant?nio
>
> 	[[alternative HTML version deleted]]
>
>

-- 
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