shapefiles, images, iimagemaps, and removinginternalboundary lines

Hi Roger,

Thanks again for the response.  To answer your questions:

- I am currently running on R 2.3.1.  I was at 2.4.x, but some of the 
packages I thought I needed weren't available on the cran interface in

the rgui (I was experimenting, and I can't remember what they were 
now, so that may no longer be true).  It sounds like you are fine 
running R at 2.4, though, and I could probably upgrade, as my sole 
purpose for having R right now is to deal with shapefiles and create

- Related to the above, I don't see the spgpc package on my mirror 
(USA (IA)), but that may be related to being at 2.3?

Also, I saw the 'unionSpatialPolygons' command in Debarchana Ghosh's 
code, but didn't know what it did.  I'll investigate the paths you 
have listed here.

Thanks again,
Matt

-----Original Message-----
From: Roger Bivand [mailto:Roger.Bivand at nhh.no]
Sent: Thursday, October 19, 2006 2:32 AM
To: Pettis, Matthew (TLR Corp)
Cc: r-sig-geo at stat.math.ethz.ch
Subject: Re: [R-sig-Geo] shapefiles, images, iimagemaps, and removing 
internalboundary lines

On Wed, 18 Oct 2006 matt.pettis at thomson.com wrote:

I have sucessfully inputted a shapefile into a 
SpatialPolygonsDataFrame object.  I would like to output this file 
as a .gif/.png/.bmp/.jpeg image and generate an imagemap for the 
outputted image.  Does anybody know the best way to approach this?

RSiteSearch("imagemap")

gets you to:

http://finzi.psych.upenn.edu/R/Rhelp02a/archive/28035.html

This installs on R 2.4.0 from source - which platform are you using 
and can you install source packages? The documentation in 
imagemap/inst/doc/imagemap-howto.pdf is clear, addRegion(im) <- for 
each clickable object. How to go from there depends on what you want 
to be clickable.

Alternatives might be Rpad:

http://finzi.psych.upenn.edu/R/Rhelp02a/archive/77952.html

or using ogr2ogr in FWTools (external software) to generate a KML for 
Google Earth (if the bubble that pops up is enough - I don't know how 
to put a link into it, though I guess it could be done), or writing 
the KML from R:

http://bbs.keyhole.com/ubb/showflat.php/Cat/0/Number/221682/Main/21913
1

 secondly (and i may need to start another thread for this), but is 
there an easy function to remove the interior lines of aggregated 
shapes (and generate an imagemap again, etc.)?  For example, If I 
have

a map of the U.S.'s with a polygon for each state, could I remove 
all internal state boundaries to leave just the national border?

Using the objects you have now, you need to install the spgpc package:

rSpatial <- "http://r-spatial.sourceforge.net/R"
install.packages("spgpc", repos=rSpatial)

and install gpclib from CRAN. Then

?unionSpatialPolygons

to dissolve internal boundaries. This is for arbitrary polygons, if 
you really just need to dissolve US states, perhaps using the CRAN 
maps package with its built-in database, and its own dissolve 
mechanism would save re-doing topology, but it only works for polygons

Roger

 
thanks,
Matt

--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School 
of Economics and Business Administration, Helleveien 30, N-5045 
Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no