[R-sig-Geo] topographic maps

[Roger Bivand]

On Wed, 25 Feb 2009, Hans-Jörg Bibiko wrote:

> Dear all,
>
> I have a tiny problem, I'd like to draw a map showing topographic information 
> (like in a normal atlas) and on top of this map some polygons, points, etc. 
> given by long, lat values.
>
> I tried the geomapdata ETOPO5 in conjuction with GEOTOPO which actually works 
> fine but the point is I'm dealing with maps displaying Eurasia and this takes 
> really time (and memory) to plot [I also set GEOTOPTO's npoints to 5 bustill 
> the same].
>
> Then I tried to use geotiff via readOGR which also works but the same here, 
> it takes too much time and I have to produce 116 maps.
>

Well, readGDAL, I hope? If so, use readGDAL(..., output.dim=) to decimate 
the image.

For display, note that the R graphics engines only output vector graphics, 
so each raster cell is drawn as a filled rectangle, which takes time. The 
trick of decimating the image on input ought to reduce the number of 
rectangles to plot.

Roger

>
>
> Is there any elegant way to have a geo-referenced image as background and 
> then to draw polygons etc. on top of it? As I said I'm dealing with Eurasia 
> thus the resolution is not the big problem.
>
> I'd be happy to get any hint.
>
> Thanks!
>
> --Hans
>
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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