I'm implementing STRIPACK, the Delaunay triangulator/Voronoi tessellator
for spheres, working from FORTRAN 77 code available via the ACM Digital
Library.  I'm also interested in displaying my data, and I have
"operationally toured" a bunch of what's available for R, including
rgdal, sp, TeachingDemos, PBSmapping, maptools, and so on.  At first I
thought a display on a sphere would be best, but I'm not sure now, as it
doesn't lend itself readily to detail or various projections, unless the
projection is built first as an image and wrapped around the sphere.

So I'm working with two dimensional displays, polysets, and the like,
still debugging.  

One thing is that some of the data I have induces triangles or tiles
that are spatially large, occupying a substantial portion of the globe,
and certainly an entire dataset wraps the globe.  That was the
characteristic which drove me to look at spheres first, but the set of
existing code and techniques for R looks richer with two dimensional
projections.  

So, what I'm thinking of is creating a display which has like 3/2 globes
in Gall projection on it, overlapping the right and left edges.  The
idea is to show as much of the tiles in an unbroken presentation as
possible.  There are three things, then, I'd like to ask suggestions
about.

First, datasets like world time zones or world coastlines get read in as
polygons at fixed places.  If I am to project on 3/2 globes, I'll need
to replicate these polydata appropriately and union the replicas onto
the base.  I can write that, but have not been able to find
documentation about what these polydata are supposed to look like, as
dataframes, for instance.  Any pointers?  Anyone done anything like
this?  I have looked at PBSmapping's descriptions of  PolySet.

Second, even if I do this, there's a chance an edge of a tile will wrap
from one side of the image to the other.  The idea of using 3/2 globes
is to minimize that when the rule chosen is to suppress the edge or tile
if this happens.  An alternative is to be able to draw the edge with the
wrapping understood by the plotter.  As these packages now seem to be
standardizing on what is basically a two dimensional display (pardon me
if I misunderstand), I'm guessing the chances of that being handled
automatically are slim.  Anyone ever do such a thing or know something
comparable, that is, displaying polygons across a "wrapping break" in a
map?  

Third, I am currently doing this awkwardness:

	dd <- data.frame(Id=identifiers.to.show, X=longitudes.to.show,
Y=latitudes.to.show)
	ddTable <-
data.frame(Id=unique(identifiers.to.show),Name=frames.to.show)
	ddShapefile <- convert.to.shapefile(dd, ddTable, "Id", 5)
	write.shapefile(ddShapefile, "stripack_prb_test_deltri",
arcgis=T)
	
	projection <- CRS("+proj=gall +lon_0=0 +x_0=0 +y_0=0")
	
	delaunayPolysSP <- readShapePoly("stripack_prb_test_deltri",
proj4string=projection)
	delaunayPolysPS <- SpatialPolygons2PolySet(delaunayPolysSP) 

	worldPolysSP <- readShapePoly("WRLDTZA", proj4string=projection)
	worldPolysPS <- SpatialPolygons2PolySet(worldPolysSP)      
	plotPolys(worldPolysPS, xlim=c(-270.,270.), ylim=c(-90.,90.),
projection=TRUE, lty="dotted")
	addPolys(delaunayPolysPS, xlim=c(-270.,270.), ylim=c(-90.,90.),
border="blue")
	
	title(main=trplot_title)
     
because I know how to create a shapefile and read a set of polygons in
from a shape file, but I don't know how to build the polygons directly?
Can someone recommend a perspicacious way of avoiding this?

Thanks,

 - Jan,
          Akamai

	[[alternative HTML version deleted]]


