Thanks for the helpful suggestion Michael.

I have done this kind of conversion from shapefile to lon-lat projection
before.

My problem now is that I would like to take lon-lat data and transform it
into a lambert conformal projection with particular parameters. What I'm
failing on is how to specify the destination projection I want. Where is
there a description of all the projection strings for things like Lambert
conformal?

...

Aha ... I found what I wanted: the PROJ strings are specified in the users
manual

ftp://ftp.remotesensing.org/proj/OF90-284.pdf

In my case I wanted Lambert conformal conic:

+proj=lcc +lon 0=90w +lat 1=20n +lat 2=60n




On Thu, Mar 15, 2012 at 5:28 PM, Michael Sumner <mdsumner@gmail.com> wrote:

> spTransform in the rgdal package will do this very simply. You just
> need the source metadata set on the original object, and spTransform
> handles the rest.
>
> From the help page:
>
> require(rgdal)
> scot_BNG <- readOGR(system.file("vectors", package = "rgdal")[1],
> "scot_BNG")
>     scot_LL <- spTransform(scot_BNG, CRS("+proj=longlat +datum=WGS84"))
>
> ## metadata is already correctly set
> proj4string(scot_BNG)
> ## [1] " +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000
> +y_0=-100000 +datum=OSGB36 +units=m +no_defs +ellps=airy
> +towgs84=446.448,-125.157,542.060,0.1502,0.2470,0.8421,-20.4894"
>
>
> class(scot_BNG)  ## "SpatialPolygonsDataFrame"
>
> ## transform (from whatever the current CRS is to any other supported
> PROJ.4 CRS)
> scot_LL <- spTransform(scot_BNG, CRS("+proj=longlat +datum=WGS84"))
>
> mapproject (in package mapproj I assume) is a much more raw interface
> for transforming from long/lat, and you might as well use ?project
> from rgdal which also can do the inverse. If you cannot install rgdal
> that's another story, but it's trivial on Windows (because of work by
> the maintainers and the R Core Team), and well documented for other
> platforms.
>
> Cheers, Mike.
>
>
> On Fri, Mar 16, 2012 at 11:15 AM, Jonathan Callahan
> <jonathan@mazamascience.com> wrote:
> > I am looking for a way to reproject data that exists in a
> > SpatialPolygonsDataFrame. (I think it's the same data as in the rworldmap
> > package.)
> >
> > I am quite familiar with mapproject() which works well the maps and
> mapdata
> > packages and am hoping there is an equivalent to mapproject() that could
> > work with SpatialPolygons data.
> >
> > Or is there a simple way to get the x an y data arrays out of the
> > SpatialPolygons?
> >
> > Thanks in advance,
> >
> > Jon
> >
> > --
> > Jonathan Callahan, PhD
> > Mazama Science
> > 206-708-5028
> > mazamascience.com
> >
> >        [[alternative HTML version deleted]]
> >
> > _______________________________________________
> > R-sig-Geo mailing list
> > R-sig-Geo@r-project.org
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>
>
>
> --
> Michael Sumner
> Institute for Marine and Antarctic Studies, University of Tasmania
> Hobart, Australia
> e-mail: mdsumner@gmail.com
>
>


-- 
Jonathan Callahan, PhD
Mazama Science
206-708-5028
mazamascience.com

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