[R-sig-Geo] polygon wraps around the world after re-projection

[Carsten Dormann]

Dear fellow R-ists,

I run into problems after re-projecting a world map because one polygon 
now wraps around the world. Is there a way to re-define (or cut in two) 
the offending polygon?


require(maptools)
require(rgdal)
data(wrld_simpl)
wrld2 <- spTransform(wrld_simpl, CRS("+proj=cea +lon_0=Central Meridian 
+lat_ts=Standard Parallel +x_0=False Easting +y_0=False Northing")) # 
change to Lamberth cylindrical equal area projection

plot(wrld2) # notice the horizontal lines in the polar North!
	
I then moved the 0-longitude towards 11.7° in order to put the breaking 
line right between Russia and Alaska.

wrld3 <- spTransform(wrld_simpl, CRS("+proj=cea +lon_0=11.7 
+lat_ts=Standard Parallel +x_0=False Easting +y_0=False

plot(wrld3)

But there still is a little Aleutian island messing up the picture.

Notice that also wrld_simpl_lessIslands in rworldmap does not solve this 
problem: there always is a wrapping polygon somewhere!

I would also happily delete it, but wouldn't know how to find the 
respective polygon within the USA (slot 209) polygons.

Any help most appreciated!

Cheers,

Carsten



-- 
Dr. Carsten F. Dormann
Department of Computational Landscape Ecology
Helmholtz Centre for Environmental Research-UFZ	
(Department Landschaftsökologie)
(Helmholtz Zentrum für Umweltforschung - UFZ)
Permoserstr. 15	
04318 Leipzig				
Germany

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