> library(maptools)
Loading required package: foreign
Loading required package: sp
Loading required package: lattice

	Note: polygon geometry computations in maptools
 	depend on the package gpclib, which has a
 	restricted licence. It is disabled by default;
 	to enable gpclib, type gpclibPermit()
 
Checking rgeos availability as gpclib substitute:
TRUE
> library(rgeos)
Loading required package: stringr
rgeos: (SVN revision 254)
 GEOS runtime version: 3.3.0-CAPI-1.7.0 
 Polygon checking: TRUE 
 WARNING! if you turn polygon checking off, and polygons are
 not valid in GEOS, you risk losing data as your R session may crash! 

> 
> sessionInfo()
R version 2.11.1 (2010-05-31) 
x86_64-redhat-linux-gnu 

locale:
 [1] LC_CTYPE=en_US.iso885915       LC_NUMERIC=C                  
 [3] LC_TIME=en_US.iso885915        LC_COLLATE=en_US.iso885915    
 [5] LC_MONETARY=C                  LC_MESSAGES=en_US.iso885915   
 [7] LC_PAPER=en_US.iso885915       LC_NAME=C                     
 [9] LC_ADDRESS=C                   LC_TELEPHONE=C                
[11] LC_MEASUREMENT=en_US.iso885915 LC_IDENTIFICATION=C           

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] rgeos_0.1-8    stringr_0.4    maptools_0.8-9 lattice_0.18-8 sp_0.9-83     
[6] foreign_0.8-40

loaded via a namespace (and not attached):
[1] grid_2.11.1 plyr_1.5.2 
> 
> de1990 <- readShapePoly("shapefiles/subset_1990_de.shp")
> de2000 <- readShapePoly("shapefiles/subset_2000_de.shp")
> 
> union <- gUnion(de1990, de2000)
Error in RGEOSBinTopoFunc(spgeom1, spgeom2, byid, id, "rgeos_union") : 
  TopologyException: no outgoing dirEdge found at -77.0822 38.9222
Calls: gUnion -> RGEOSBinTopoFunc -> .Call
Execution halted


End of R job:  completed with errors in 6 seconds.

