Although I'm interested many of the issues below, and also feel the attraction of the develop-it-ourself, my personal agenda is a bit more modest. Once we start with GEOS support (an idea mentioned every 6 months on this list), the next thing we need for dealing with huge or massive data sets is a clever indexing structure. After that, full topology. I find it hard to imagine where the resources should come from for all these things that are available in OSGeo next door -- we can't settle with proof of concepts, but want quality stuff. OTOH, one day a student may come in who just finished two of these projects.
My primary goal is to get sp stable, and adopted by more of the numerous packages for analyzing spatial data in R. And yes, I did introduce an instabillity this week -- try [ on a SpatialPolygonsDataFrame with NA values in the row index. There's a lot of code, much of which is little tested and/or not very clean. Another goals is to get a good and smooth system where R works as a back-end in interopable systems, possibly using PostGIS to transfer data. Finally: further proof that R is a increasingly wonderful system for analyzinig spatial data. -- Edzer [EMAIL PROTECTED] wrote: > The thread below and many others in R-sig-Geo raise questions about > future directions. In reinventing GIS there are a whole list of > capabilities and functions that would be helpful. Some that I have > noticed include, > > Topological representation to enable > Planar enforcement of boundary integrity of polygon tessellations > "Dissolving" interior edges easily as in the thread below > Large problem computational geometry functions > Identify many points inside of many polygons > Intersections/overlays of two sets of many polygons > Distances between all pairs of many polygons > > Are there members of the R Geo community working on any of these? > Are these issues seen as an exclusive focus of commercial GIS? > Are there discussions about these issues at relevant conferences? > > (I will be at AAG in San Francisco and would be happy to meet with > others if there is interest.) > > [EMAIL PROTECTED] wrote on 2007-03-16 07:52:59: > > >> Hi Tim, >> You could compute the convex hull first, and then iterate from points >> on the convex hull. That should be much faster already, especially >> > since > >> hexagons are convex and the perimeter will be locally convex around >> > all > >> the >> points touching the convex hull. You could do a variation >> of the "monotone pieces" algorithm that is used in computational >> geometry. >> But this is a simpler problem. Are there cases with interior holes? >> >> I have been meaning to write something like this for hexbin for a >> > while. > >> There >> are many cases where it would be nice to find approximations to the >> density contours >> and a quick and dirty way is to threshold the hexagon counts, find the >> hull and >> smooth the perimeter. >> >> Nicholas >> >> On Fri, 16 Mar 2007 08:34:20 -0500, "Tim Keitt" <[EMAIL PROTECTED]> >> > said: > >>> Hi Nic, >>> >>> The convex hull would be fast and easy to compute (there's existing >>> code in R). I want the ordinary hull which is the set of arcs >>> > forming > >>> the perimeters (inside and out). My crude and very slow solution was >>> to convert all the polygons (in this case hexagons on a lattice) >>> > into > >>> their constituent arcs and then for each arc count how many times it >>> occurs in the set (requires slightly fuzzy matching of points). Arcs >>> that occur more than once are removed. The remaining arcs form the >>> hull. Runs in about 20 minutes with a few hundred hexagons. >>> Sufficient for the moment. >>> >>> THK >>> >>> On 3/16/07, Nicholas Lewin-Koh <[EMAIL PROTECTED]> wrote: >>> >>>> Hi Tim, >>>> I am not quite sure what you are getting at here. Do you want to >>>> intersect >>>> polygons and then select the set of lines that form the outer >>>> > perimeter? > >>>> Do you wan the convex hull of a set of polygons. I guess I have >>>> > been out > >>>> of the >>>> GIS world to long. It seems to me that this would be something >>>> > easy to > >>>> solve, >>>> just tedious iteration of the polygon coordinates and some >>>> triangulation. >>>> >>>> Nicholas >>>> >>>> >>>>> Date: Thu, 15 Mar 2007 10:49:23 -0500 >>>>> From: "Tim Keitt" <[EMAIL PROTECTED]> >>>>> Subject: [R-sig-Geo] polygons to arcs? >>>>> To: r-sig-geo@stat.math.ethz.ch >>>>> Message-ID: >>>>> >>>>> > <[EMAIL PROTECTED]> > >>>>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed >>>>> >>>>> Is there an 'sp' function that takes a polygon as its argument >>>>> > and > >>>>> returns a set of line objects corresponding to the arcs in the >>>>> polygon? >>>>> >>>>> Or better yet, a function that given a set of polygons, returns >>>>> > the > >>>>> hull? (ie the set of singleton arcs after applying the polys to >>>>> > arcs > >>>>> function) >>>>> >>>>> THK >>>>> >>>>> -- >>>>> Timothy H. Keitt, University of Texas at Austin >>>>> Contact info and schedule at http://www.keittlab.org/tkeitt/ >>>>> Reprints at http://www.keittlab.org/tkeitt/papers/ >>>>> ODF attachment? See http://www.openoffice.org/ >>>>> >>>>> >>>>> >>>>> >>> -- >>> Timothy H. Keitt, University of Texas at Austin >>> Contact info and schedule at http://www.keittlab.org/tkeitt/ >>> Reprints at http://www.keittlab.org/tkeitt/papers/ >>> ODF attachment? See http://www.openoffice.org/ >>> >> _______________________________________________ >> R-sig-Geo mailing list >> R-sig-Geo@stat.math.ethz.ch >> https://stat.ethz.ch/mailman/listinfo/r-sig-geo >> > > _______________________________________________ > R-sig-Geo mailing list > R-sig-Geo@stat.math.ethz.ch > https://stat.ethz.ch/mailman/listinfo/r-sig-geo > _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
