Sampling random plots
On Fri, 26 Oct 2007, Gerald Jurasinski wrote:
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)
You can just do spsample(sr, ...), which will traverse your object to get to the single Polygon, sr is what class(sr) says.
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?
Because the external dependencies for the many OSX versions and platforms are too complicated for the CRAN OSX builder to support. Please follow the instructions on: http://www.sal.uiuc.edu/tools/tools-sum/rgeo/rgeo-detail/map-packages-on-cran to build from source. 32-bit Windows is simpler to support because there are fewer moving targets, and Uwe Ligges has been very generous in helping to automate the build process. Roger
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 at uni-rostock.de
http://www.auf.uni-rostock.de/loe
+49 381 4983225 (tel)
+49 381 4983222 (fax)
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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