I've finally done this operation with a GIS. I was trying to perform all this part of the project within R, trying not to use any other tool, as a test. It's clear that the boundary between GIS and spatial analysis is more and more fuzzy. In my opinion, just importing and exporting between R and a GIS (i.e. grass) is getting increasingly inconvenient, as the GIS operations become more an more intermixed with the analysis. Perhaps the direct integration of R and Qgis could be a solution (if at least direct display of R spatial objects in QGis were possible!). But, at this point, I don't know if this particular operation (dividing the polygon into two by a line) could have been done in QGis. I used a commercial vector-based software just because it's the the tool we normally use and could not put more time in exploring this issue.
Thanks! Agus Roger Bivand escribió: > On Tue, 30 Oct 2007, Agustin Lobo wrote: > >> Is it possible to divide a polygon by a line >> into 2 polygons? > > No, in general. All computational geometry ends up in having to deal > with the type of polygon. A convex polygon is one thing, and can be > divided into two parts, but a general polygon may be concave, and the > number of parts does not have to be two - the line could cross it > multiple times. The approach taken in the Rgshhs function in maptools is > to overlay a rectangular box over the polygon(s), and see what comes > out, but quite often it isn't two (or in that case a single part within > the rectangle). > > Roger > >> >> Agus >> > -- Dr. Agustin Lobo Institut de Ciencies de la Terra "Jaume Almera" (CSIC) LLuis Sole Sabaris s/n 08028 Barcelona Spain Tel. 34 934095410 Fax. 34 934110012 email: [EMAIL PROTECTED] http://www.ija.csic.es/gt/obster _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo