Hi, Just a question to try and understand where the problem comes from: Are the lines correctly represented in the shape files (and the problems comes when importing/processing it), or is it already buggy in the shape files?
Also, you might want to look at the solution I use since I have the same application as you and it works perfectly with a Qgis-R tandem. I have lines as a shp layer in a QuantumGIS project, with distinct attributes for each lines. I use the "manageR" plugin to transfer data (line and DEM) to R: http://www.ftools.ca/plugins.html Then I created a "manageR" plugin (using library spatstat among others) to sample along a line to get the profile according to DEM. It works nicely. For the moment, it's only available at the link below, but you can copy-paste to the tools.xml file: http://code.google.com/p/ftools-qgis/source/detail?r=150 http://code.google.com/p/ftools-qgis/source/detail?r=151 (because of xml, the "<-" sign is represented as "<-") Hope it helps, Mayeul _____________________________________________________ Dr. Mayeul KAUFFMANN, Conflict Specialist European Commission, Joint Research Centre (JRC) Institute for the Protection and Security of the Citizen (IPSC) Global Security and Crisis Management - ISFEREA Via E. Fermi 2749 - I-21027 Ispra (VA), ITALY Phone: (+39) 033278 5071 http://isferea.jrc.ec.europa.eu/Staff/Pages/Kauffmann-Mayeul.aspx (Office: building 48c, 1st floor, room 123. TP: 483) -----Original Message----- From: r-sig-geo-boun...@stat.math.ethz.ch [mailto:r-sig-geo-boun...@stat.math.ethz.ch] On Behalf Of Roger Bivand Sent: Thursday, June 17, 2010 11:51 AM To: Don MacQueen Cc: r-sig-geo@stat.math.ethz.ch; Colin Rundel Subject: Re: [R-sig-Geo] Combining multiple polylines into a single polyline On Sat, 12 Jun 2010, Don MacQueen wrote: > I have an input shapefile representing roads in a city, read into R where it > becomes a SpatialLInesDataFrame. > > Looking at just one road at a time, it looks fine when plotted. But in the > underlying structure, the single real-world road has been broken up into many > shorter polylines, and they are not included in the "correct" order, i.e., > end to end. Is this an rgeos question - you seem to need a topology operation on geometries? Since rgeos is work in progress, there isn't support yet, and I don't know if there will be, but the use case seems convincing. Roger > > When I sample along the road using spsample() with type='regular', the points > aren't equally spaced. I assumed this was because it is broken up into > separate lines. So I thought to combine the many short polylines into a > single long polyline, i.e., matching endpoints of one polyline with the > beginning of the next, dropping redundant nodes, and creating a new SLDF > object. > > I'm wondering if there's already an algorithm for this somewhere (in R or > GRASS, preferably!). > (That's my main question) > > > However, in my toy example below, consisting of just three polylines making > up a single road, spsample() does appear to equally space the points along > the entire length. So perhaps my real roads have some other structural > problem. Perhaps some endpoints don't match. > > Thanks > -Don > > Here's a toy example: > > l1 <- matrix(c(1,1, 6,6, 4,8), byrow=TRUE, ncol=2) > l2 <- matrix(c(4,8, 7,9), byrow=TRUE, ncol=2) > l3 <- matrix(c(7,9, 11,10, 13,13), byrow=TRUE, ncol=2) > > LL1 <- Lines( list( Line(l1)) , ID='32') > LL2 <- Lines( list( Line(l2)) , ID='147') > LL3 <- Lines( list( Line(l3)) , ID='21') > > ## deliberately constructed out of order > SL <- SpatialLines( list( LL2, LL3, LL1) ) > df <- data.frame( name=rep('Road',3)) > row.names(df) <- c('147','21','32') > SLDF <- SpatialLinesDataFrame( SL, df) > > ## I would like to reduce to a structure like this: > lc <- rbind(l1 , l2[-1,] , l3[-1,]) > df1 <- data.frame( name='Road') > row.names(df1) <- 'a' > SLDFfix <- SpatialLinesDataFrame( SpatialLines( list( Lines( list( Line(lc)) > , ID='a'))) , df1) > > -- 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.biv...@nhh.no _______________________________________________ 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
