Could you please let me know more details about rgval package? I have never
used it before. I only tried image.plot() where if you have regular lat and
lon, a map() function can be used later to overlay state map onto it.

On 4/5/07, Roger Bivand <Roger.Bivand@nhh.no> wrote:
>
> On Thu, 5 Apr 2007, Vladimir Eremeev wrote:
>
> >
> > If your country or state borders are polygons or polylines, you could
> > convert them to desired projection using the function project from the
> > package rgdal.
> >
> > Latitude-longitude grid also could be added by generating desired
> > polylines in lat-lon and converting them to the desired projection using
> > project.
> >
>
> Yes, the route would be to plot the image in its native projection, and
> project the vector data (shorelines, countries) to the same projection.
> Similar topics have been discussed on the R-sig-geo list, including the
> reading of netcdf files (which are a bit picky) with functions in the
> rgdal package which import the coordinate reference system directly.
>
> Please follow this up on R-sig-geo if you need more help.
>
> >
> > Linda Smith wrote:
> > >
> > > I have a netcdf gridded file with LCC projection. I can easily use
> > > image.plot to visualize it. However, as the axises are in X,Y, not Lat
> and
> > > Lon, I could not add state or country maps onto it (or lat lon
> > > information).
> > > I do have a grid2d file that describes the lat and lon for each (X,Y)
> > > grid,
> > > but the lat and lon are not regularly spaced, so I could not use
> > > image.plot.
> > >
> > > Does anyone know how to plot this type of gridded data so that country
> or
> > > state borders can be easily added? Thanks a lot!
> > >
> >
> > What do you mean by "grid2d file that describes the lat and lon for each
> > (X,Y) grid"?
> > If this are two rasters of the same size having corresponding latitude
> and
> > longitude values in each raster cell, then you could use contourLines to
> get
> > lat-lon grid. However, you, probably, will want to smooth it.
> >
>
> --
> 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@nhh.no
>
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