R help - Apr 2007 - how to image.plot a XY grid file into a lat-lon map

Hi All,

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!

Linda

	[[alternative HTML version deleted]]

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.


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.
-- 
View this message in context:
http://www.nabble.com/how-to-image.plot-a-XY-grid-file-into-a-lat-lon-map-tf3528721.html#a9852612
Sent from the R help mailing list archive at Nabble.com.

http://r-spatial.sourceforge.net



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!
> 
> Linda
> 
-- 
View this message in context:
http://www.nabble.com/how-to-image.plot-a-XY-grid-file-into-a-lat-lon-map-tf3528721.html#a9852804
Sent from the R help mailing list archive at Nabble.com.

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 at nhh.no

Hello Linda,

Friday, April 6, 2007, 2:47:43 AM, you wrote:

LS> On 4/5/07, Vladimir Eremeev <wl2776 at gmail.com> wrote:
VE>> If your country or state borders are polygons or polylines, you could
convert
VE>> them to desired projection using
VE>> the function project from the package rgdal.

VE>> Latitude-longitude grid also could be added by generating desired
polylines
VE>> in lat-lon and converting them to the desired projection using
project.


LS> Linda Smith wrote:

LS>>> I have a netcdf gridded file with LCC projection. I can easily
use
LS>>> image.plot to visualize it. However, as the axises are in X,Y,
not Lat and
LS>>> Lon, I could not add state or country maps onto it (or lat lon
LS>>> information).
LS>>> I do have a grid2d file that describes the lat and lon for each
(X,Y)
LS>>> grid,
LS>>> but the lat and lon are not regularly spaced, so I could not use
LS>>> image.plot.
LS>>>
LS>>> Does anyone know how to plot this type of gridded data so that
country or
LS>>> state borders can be easily added? Thanks a lot!
LS>>>

VE>> What do you mean by "grid2d file that describes the lat and lon
for each
VE>> (X,Y) grid"?
VE>> If this are two rasters of the same size having corresponding
latitude and
VE>> longitude values in each raster cell, then you could use contourLines
to get
VE>> lat-lon grid. However, you, probably, will want to smooth it.

LS> Yes, they are. I could add lat and lon info?that way, but
LS> still I could not use map() function to overlay state borders onto
LS> my image plot because this image is not? in lat and lon
LS> coordinates.


I presume you are using the function map() from the maps package.
?map says that it returns a list with x, y, range, and names
components.
You could do something like following, for example (UNTESTED).

  state.borders.ll<-map("state",plot=FALSE)
 
state.borders<-project(cbind(state.borders.ll$x,state.borders.ll$y),proj="+proj=lcc
+lat_1=48 +lat_2=33 +lon_0=-100")
  lines(state.borders)

-- 
Best regards,
 Vladimir                            mailto:wl2776 at gmail.com


--SevinMail--

Does anybody know how to write the code for extracting value of  LAGRANGE
MULTIPLIER after ordinary prediction in "gstat" in R?

Thanks!

Zia


-- 
Zia Uddin Ahmed
915 Brad Field Hall
Department of Crop and Soil
Cornell University
Ithaca NY 14850
USA