Dear List,

Could someone please help me, with a tiny question?

I have read in a shapefile with readShapePoly:
sr <- readShapePoly("study_region")

It just contains of one polygon.

As i would like to sample random locations inside i do:
 > sr.pts <- sample.Polygon(sr, 60)

However, the function tells me, that there is no "area" slot in the  
object:
Error in getPolygonAreaSlot(x) : no Slot of name "area" for this  
object of class "SpatialPolygonsDataFrame".

But when looking at the object, there is a slot called "area" (see  
below). Do i have to convert the sr object to another spatial object  
which can better be handled by package sp functions (because it was  
read in with a maptools function)? And by the way, why there is no  
rgdal binary for mac on CRAN?


 > sr
An object of class “SpatialPolygonsDataFrame”
Slot "data":
   Id
0  0

Slot "polygons":
[[1]]
An object of class “Polygons”
Slot "Polygons":
[[1]]
An object of class “Polygon”
Slot "labpt":
[1] 4510732 6009121

Slot "area":
[1] 250264.9

Slot "hole":
[1] FALSE

Slot "ringDir":
[1] 1

Slot "coords":
          [,1]    [,2]
  [1,] 4510328 6008870
  [2,] 4510339 6008963
  [3,] 4510347 6009007
  [4,] 4510371 6009123
  [5,] 4510386 6009155
  [6,] 4510427 6009198
  [7,] 4510456 6009218
  [8,] 4510536 6009269
  [9,] 4510590 6009324
[10,] 4510655 6009395
[11,] 4510704 6009380
[12,] 4510752 6009358
[13,] 4510899 6009300
[14,] 4511018 6009246
[15,] 4511127 6009077
[16,] 4511246 6009065
[17,] 4511343 6009053
[18,] 4511213 6008975
[19,] 4511176 6008970
[20,] 4511123 6008980
[21,] 4511077 6009002
[22,] 4511007 6009021
[23,] 4510939 6009028
[24,] 4510866 6009021
[25,] 4510790 6009007
[26,] 4510723 6008985
[27,] 4510643 6008953
[28,] 4510579 6008934
[29,] 4510510 6008921
[30,] 4510420 6008893
[31,] 4510328 6008870



Slot "plotOrder":
[1] 1

Slot "labpt":
[1] 4510732 6009121

Slot "ID":
[1] "0"

Slot "area":
[1] 250264.9



Slot "plotOrder":
[1] 1

Slot "bbox":
        min     max
r1 4510328 4511343
r2 6008870 6009395

Slot "proj4string":
CRS arguments: NA



——————————————————

Dr. Gerald Jurasinski
Landscape Ecology and Site Evaluation
Institute for Management of Rural Areas
Faculty of Agricultural and Environmental Sciences
University of Rostock
Justus-von-Liebig-Weg 6
18059 Rostock
Germany

gerald.jurasinski@uni-rostock.de
http://www.auf.uni-rostock.de/loe
+49 381 4983225 (tel)
+49 381 4983222 (fax)



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