[R] png misbehaving with levelplot when inside a loop

[Paul Hiemstra]

Hi David,

Putting a print statement around your spplot command solves your 
problem. This behaviour is common for trellis graphics plot methods 
(such as spplot). This is the command including print:

  print(spplot(meuse, c("ffreq"), 
sp.layout=list(l2,l3,l4,l5),col.regions="black",pch=c(1,2,3),
         key.space=list(x=0.1,y=.95,corner=c(0,1))))

These kinds of questions maybe are not specific to sp, but still might 
generate more response from the r-sig-geo mailing list.

cheers,
Paul

David wrote:
> I want to use spplot inside a loop  to itteratively produce png files.
>
>
> for (i in 1:5){
>   png(file=paste("myPlot",i,".png",sep=""),bg="white",height=500,width=500)
>   library(lattice)
>   trellis.par.set(sp.theme()) # sets bpy.colors() ramp
>   data(meuse)
>   coordinates(meuse) <- ~x+y
>   l2 = list("SpatialPolygonsRescale", layout.north.arrow(), offset = c(181300,329800), scale = 400)
>   l3 = list("SpatialPolygonsRescale", layout.scale.bar(), offset = c(180500,329800),
>     scale = 500, fill=c("transparent","black"))
>   l4 = list("sp.text", c(180500,329900), "0")
>   l5 = list("sp.text", c(181000,329900), "500 m")
>   spplot(meuse, c("ffreq"), sp.layout=list(l2,l3,l4,l5),col.regions="black",pch=c(1,2,3),
>          key.space=list(x=0.1,y=.95,corner=c(0,1)))
>   dev.off()
> }
>
> The above example fails to write the output to the file. When the loop
> is finished the file size of each file is 0Kb. If I perform the work
> of the loop manually, ie. setting "i <- 1", "i <- 2" etc before
> manually running the loop contents then there is no problem.  There is
> also no problem if I replace all the spplot stuff with say
> "hist(rnorm(100))".
>
> The same behaviour is reproduced with levelplot too so is not sp specific.
>
> for (i in 1:5){
>   png(file=paste("sillyPlot",i,".png",sep=""),bg="white",height=500,width=500)
>   x <- seq(pi/4, 5 * pi, length = 100)
>   y <- seq(pi/4, 5 * pi, length = 100)
>   r <- as.vector(sqrt(outer(x^2, y^2, "+")))
>   grid <- expand.grid(x=x, y=y)
>   grid$z <- cos(r^2) * exp(-r/(pi^3))
>   levelplot(z~x*y, grid, cuts = 50, scales=list(log="e"), xlab="",
>             ylab="", main="Weird Function", sub="with log scales",
>             colorkey = FALSE, region = TRUE)
>   dev.off()
> }
>
> How should I correctly write these loops to do as intended?
>
> cheers
> David
>
>
>
>   


-- 
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