[R-sig-Geo] symbols on a map

[Susumu Tanimura]

Hi there,

My today's trial is to put symbols on a map.  After reading pnm files
(airport symbol) with read.pnm() from pixmap package, I overlaid the pixmap
objects on the map following their xy coordinates.

library(maptools)
library(pixmap)
airport <- function() {
  A <- "airp.shp"
  V <- "admin1.shp"
  plot((read.shape(V)))
  r <- read.pnm("air.ppm")
  a <- Map2points(read.shape(A))
  for (i in 1:length(a[,1])) addlogo(r,px=c(a[i,1]-0.5,a[i,1]+0.5),py=c(a[i,2]-0.5,a[i,2]+0.5))
}

Unfortunately, resulted map was very ugly because the pnm format dose
not have transparency.  For mapping purpose, treating with a picture
format with alpha channel is needed.  Dose anyone succeed to put
symbols on a map of R?

It may very happy if I can use metapost, eps, or any other vector
formats for symbology of map.

--
Susumu Tanimura