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

Tue, 12 Aug 2008 09:51:44 -0700 

Edzer Pebesma wrote:

No, it's me, I only read half of your question. Try something like

spplot(spdf["dist"], sp.layout=list("sp.polygons", river))

or the incremental build, in lattice style, of

spplot(spdf["dist"])
library(lattice)
spplot(spdf["dist"])
trellis.focus("panel", 1, 1)
sp.polygons(river)
trellis.unfocus()
which will put the river on the foreground. This can be obtained in a single pass with 

spplot(spdf["dist"], sp.layout=list("sp.polygons", river, first=FALSE))

Edzer,
The first = argument is not documented when I type ?sp.polygons or ?panel.gridplot. You can only see it if you look at the source code of panel.gridplot. A very flexible way of adding layout objects is to define the panel function directly like (as shown on the R Wiki (http://wiki.r-project.org/rwiki/doku.php?id=tips:spatial-data:spatial_data_visualization)): 

spplot(grid_object, "layer_to_plot",
   panel = function(...) {
       panel.gridplot(...)
       sp.polygons(polygon_object)
       sp.points(point_object)
   }
That was my solution to draw the polygons on top of the grid. I started a Spatial Data Visualization topic a the R Wiki (see the link above), maybe if people keep expanding that with useful topics and examples that would provide a place that makes plotting spatial objects a more accessible topic. 

cheers,
Paul
I slowly get the feeling that spplot needs a bit more documentation, or examples. 
--
Edzer

Ryan Anderson wrote:

That likely gives me the control over the color ramp that I am looking
for, but I still have trouble plotting the vector layer over the top of
the resulting image plot.
If I do:
 spplot(spdf["dist"],col.regions=heat.colors(400), at = 0:10/10)
 plot(river, add = TRUE)
I still get the plot.new has not been called yet error after I attempt to 
add the river data.  What am I doing wrong?

Thanks,
Ryan



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/









--
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone:  +31302535773
Fax:    +31302531145
http://intamap.geo.uu.nl/~paul

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