[R-sig-Geo] generate & plot elevation contour lines

[Edzer J. Pebesma]

karl.sommer at dpi.vic.gov.au wrote:
>
> Eventually I had success with the following construct.
>
> CL <- contourLines2SLDF(contourLines(as.image.SpatialGridDataFrame
>       (as(topo.idw["var1.pred"],"SpatialGridDataFrame"))))
> I then passed CL using sp.layout and it worked
>
> The next challenge is how to pass the corresponding labels ?
>   
Not so much to pass them, as they are attributes in the
SpatialLinesDataFrame object; the challenge is to plot
them at suitable locations.

contour() does this quite differently from contourplot()
in lattice it seems, but the former uses some non-accesible
function through .Internal().
--
Edzer