[R-sig-Geo] Plotting polygons on top of a levelplot

[Edzer Pebesma]

Ryan, you're probably looking for something like

spplot(spdf["dist"],col.regions=heat.colors(400), at = 0:10/10)

spplot is a wrapper around lattice functions for spatial data, and tries 
to pass on all the lattice controls.
--
Edzer

Ryan Anderson wrote:
> I have some gridded spatial data that I want to plot with a vector overlay
> on top.  The following reproducible code makes a figure similar to the one
> I am ultimately trying to produce:
>
> library(sp)
> library(fields)
> data(meuse.grid)
> data(meuse.riv)
> coords <- SpatialPixels(SpatialPoints(meuse.grid[, c("x","y")]))
> spdf <- SpatialPixelsDataFrame(coords, meuse.grid)
> fullgrid(spdf)<-TRUE
> river<-SpatialPolygons(list(Polygons(list(Polygon(meuse.riv)),"meuse.riv")))
> par(mar = c(5,5,5,8), col.axis = 1)
> ramp = heat.colors(400)
> image(spdf, "dist", axes = TRUE, col = ramp)
> plot(river, add = TRUE)
> zvals<-spdf$dist
> zvals<-zvals[!is.na(zvals)]
> image.plot(zlim = c(min(zvals), max(zvals)), nlevel = 256, legend.only =
> TRUE, col = ramp)
>
> I need more control over the legend and the color ramp than I know how to
> achieve with this code.  I can create the plot I want with levelplot by
> setting the 'at' component 'colorkey', but when I try to overlay the
> vector file I get an error.  Here is a simplified version of the code I
> tried:
>
> #try a levelplot
> library(lattice)
> x11()
> par(mar = c(5,5,5,8))
> x<-spdf$x
> y<-spdf$y
> z<-spdf$dist
> levelplot(z~x+y)
> plot(river, add = TRUE)
> #Gives Error in polygon(x = x, y = y, border = border, col = col, lty =
> #lty,  :
> #  plot.new has not been called yet
>
> I need to either find a way to control the mapping of data values to the
> color ramp more precisely in my call to image or image.plot or to find a
> way to plot a ploygon over the top of a levelplot.
>
> My color ramp goals more specifically: my grid contains both positive and
> negative values, and they are not necessarily symmetrically distributed
> around zero.  I want to plot them so that zero is white, negative values
> are symbolized with a ramp from white to blue (with darker shades for
> lower values) and positive values are symbolized with a ramp from white to
> red (with darker shades for higher values).
>
> Thanks for your help!
>
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>   

-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster,
Weseler Straße 253, 48151 Münster, Germany.  Phone: +49 251
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de/