R help - Apr 2010 - maptools-export owin as shapefile, error message

Hello R users,

I am trying to export an object of class "owin" from the Spatstat
package to
an ESRI shapefile using the package Maptools. I am using the function
"writePolyShape";  "pointsp" is an object of class
"ppp", "ripras" is a
function in SpatStat that creates a polygon around points. I have tried with
several different owin objects and each time I get the same error, as
follows.

 x=ripras(pointsp,shape="convex")
> xpoly=as(x,"SpatialPolygons")
> xpolyframe=as(xpoly,"SpatialPolygonsDataFrame")
> class(xpolyframe)
[1] "SpatialPolygonsDataFrame"
attr(,"package")
[1] "sp"
> writePolyShape(xpolyframe,"pgon")
Error in write.polylistShape(pls, df, file = fn, factor2char = factor2char,
:
  different number of rows in polylist and data frame


thanks for any help,

Tom Elliott, Central Washington University
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