[R-sig-Geo] problems drawing a world map on a levelplot

[Michael Sumner]

I happened to write this yesterday, which switches the parts of
wrld_simpl from < 0 longitude to the east (Pacific view). I haven't
investigated what you need in detail, so just ignore if I'm off track.

It's not careful about data or anything, since all I needed was the
raw geometry. It might be of use. "xrange" here can be anything from
[-180, 360] though it's really assuming you don't traverse more than
360 in total.

It would be nice to carefully clean up a copy of wrld_simpl like this
and make a wrld_simpl version like the maps package has.

Cheers, Mike.


xrange <- c(140, 250)
##xrange <- c(0, 360)
yrange <- c(-60, 20)

require(maptools)
require(raster)
require(rgeos)



    ext <- extent(xrange[1], xrange[2], yrange[1], yrange[2])
    data(wrld_simpl, package = "maptools")
    if (xrange[2] > 180.0) {

        eastrange <- c(xrange[1], 180.0)
        westrange <- c(-180.0, xrange[2] - 360)

        ew <- extent(westrange[1], westrange[2], yrange[1], yrange[2])
        ee <- extent(eastrange[1], eastrange[2], yrange[1], yrange[2])

        geome <- as(ee, "SpatialPolygons")
        geomw <- as(ew, "SpatialPolygons")

        ## why does this get dropped?
        proj4string(geome) <- CRS(proj4string(wrld_simpl))
        proj4string(geomw) <- CRS(proj4string(wrld_simpl))

        worlde <- gIntersection(wrld_simpl, geome)
        worldw <- gIntersection(wrld_simpl, geomw)
        worldw <- elide(worldw, shift = c(360.0, 0.0))

        proj4string(worldw) <- CRS(proj4string(wrld_simpl))

        dfe <- data.frame(x = seq_len(length(worlde at polygons)))
        dfw <- data.frame(x = seq_len(length(worldw at polygons)))
        rownames(dfw) <- as.character(as.numeric(rownames(dfe)) + nrow(dfe))

        worlde <- SpatialPolygonsDataFrame(worlde, dfe, match.ID = FALSE)
        worldw <- SpatialPolygonsDataFrame(worldw, dfw, match.ID = FALSE)
        worldw <- spChFIDs(worldw, rownames(dfw))

        world <- spRbind(worlde, worldw)

    } else {

        geom <- as(ext, "SpatialPolygons")
        proj4string(geom) <- CRS(proj4string(wrld_simpl))
        ## TODO: make this spdf if needed
        world <- gIntersection(wrld_simpl, geom)
    }


plot(world)



On Tue, Dec 18, 2012 at 8:15 PM, Tom Roche <Tom_Roche at pobox.com> wrote:
>
> summary: I've tried several ways to draw wrld_simpl over global data
> plotted with rasterVis::levelplot, but keep encountering the same
> problem:
>
> - only the eastern hemisphere of the map plots
>
> - the eastern hemisphere of the map overlays the western hemisphere of
>   the data
>
> How to fix? or otherwise provide geographical context?
>
> details:
>
> (I'll attempt to produce a "complete, self-contained example" after I
> make the code publicly viewable, but for now, I'm hoping the problem is
> sufficiently simple to diagnose.)
>
> I have atmospheric data in a netCDF file specifying gas concentrations
> over a 3D space with dimensions longitude, latitude, and (vertical)
> level, such that
>
> * the horizontal extents are global
>
> * the vertical coordinates are pressures (specifically hybrid
>   sigma-pressure)
>
> package=raster provides very usable API for loading the data into a
> RasterBrick, and package=rasterVis makes it relatively easy to levelplot
> the data in a single "atmospheric column" with the highest pressures at
> the bottom. However I also want to provide some geographic context
> (e.g., to overlay the data with national boundaries), and have failed to
> date.
>
> I have done this with maptools::wrld_simpl successfully in other
> contexts, i.e.,
>
> * loading the data with package=ncdf4 (which is considerably more work)
> * converting the data to a data.frame
> * lattice::levelplot-ing the data
> * lattice::xyplot-ing the map
>
> But when I do
>
> data(wrld_simpl)
> global.raster <- brick(in.fp, varname=data.var.name)
> layers.n <- nbands(global.raster)
> global.data.df <- as.data.frame(global.raster)
> # some twiddling of names(global.data.df) omitted
> global.map <- map('world', plot=FALSE)
> global.map.df <- data.frame(lon=global.map$x, lat=global.map$y)
> pdf(file=pdf.fp, width=5, height=100)
> # using rasterVis::levelplot, not lattice::levelplot
> levelplot(global.raster,
>   margin=FALSE,
>   names.attr=names(global.data.df),
>   layout=c(1,layers.n), # all layers in one "atmospheric column"
> ) + xyplot(lat ~ lon, global.map.df, type='l', lty=1, lwd=1, col='black')
> dev.off()
>
> the data plots apparently correctly, but the map plots incorrectly, as
> shown by this .png of the top level:
>
> https://docs.google.com/open?id=0BzDAFHgIxRzKOVdlSDFMR29BdWM
>
> As noted above, the map's eastern hemisphere overlays the data's western
> hemisphere, and nothing overlays the data's eastern hemisphere.
>
> I tried several variations on the above, but either got the same
> results, or outright error. (Unfortunately the error messages are often
> printed on the levelplot, but the messages are truncated (so they can't
> be understood), and it's annoying to "fail slow" (after waiting for a
> long plot to finish).) So after some research I sought to emulate the
> means recommended @
>
> http://rastervis.r-forge.r-project.org/#levelplot
>
> data(wrld_simpl)
> global.raster <- brick(in.fp, varname=data.var.name)
> layers.n <- nbands(global.raster)
> global.data.df <- as.data.frame(global.raster)
> # some twiddling of names(global.data.df) omitted
> global.map.proj <- CRS('+proj=latlon +ellps=WGS84')
> global.map <- map('world', plot=FALSE)
> global.map.shp <- map2SpatialLines(global.map, proj4string=global.map.proj)
> pdf(file=pdf.fp, width=5, height=100)
> # using rasterVis::levelplot, not lattice::levelplot
> levelplot(global.raster,
>   margin=FALSE,
>   names.attr=names(global.data.df),
>   layout=c(1,layers.n), # all layers in one "atmospheric column"
> ) + layer(sp.lines(global.map.shp, lwd=0.8, col='darkgray'))
> dev.off()
>
> This also fails, and very similarly (though the line colors differ). See
> this .png:
>
> https://docs.google.com/open?id=0BzDAFHgIxRzKYzd6cVB2TDE4RE0
>
> I'm guessing I can either do something simple to wrld_simpl's longitude
> values, or Something Completely Different that would Just Work Better,
> but don't know. Your assistance is appreciated.
>
> TIA, Tom Roche <Tom_Roche at pobox.com>
>
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-- 
Michael Sumner
Hobart, Australia
e-mail: mdsumner at gmail.com