[R-sig-Geo] shapefiles, images, iimagemaps, and removing internalboundary lines

[matt.pettis at thomson.com]

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 image maps.

- 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/219131

>  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 in the database.

Roger

>  
> thanks,
> Matt
> 
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> 

--
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