seamless maps

On Thu, 8 Jan 2009, Matt Oliver wrote:

Hans,

Take a look at the proj4 package, specifically project()

Or rather rgdal, which is a fully featured implementation with a  
proper interface to the PROJ.4 library. Unfortunately, there does  
not seem to be a way of shifting the prime meridian in a helpful way  
- and the original question was not about projection, but about  
joining +180 to -180, which is obvious in spherical but not in  
planar terms. rgdal provides methods for projection and datum  
transformation for objects defined in the sp package, as well as for  
projection of matrices of coordinates.

Thanks! I'm just playing with it.
Actually I do need the polygons as well.

A VERY quick&dirty&crude solution would be to pack the wrld_simpl  
polygons three times in a new SpatialPolygons object:

-the original one from -180 to 180
-a transformed one from 180 to 540
-a transformed one from -540 to -180

then by specifying xlim only one should be able to center the map for  
any longitude (to get only that clipping).
But I know it's a crude approach and then if one wants to put  
additional points/lines/etc. on it one has to treble them as well.

But anyway, thanks so much for the hints. If I found a way I'll post it.

--Hans

**********************************************************
Hans-Joerg Bibiko
Max Planck Institute for Evolutionary Anthropology
Department of Linguistics
Deutscher Platz 6     phone:   +49 (0) 341 3550 341
D-04103 Leipzig       fax:     +49 (0) 341 3550 333
Germany               e-mail:  bibiko at eva.mpg.de