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POHow to get a SpatialPolygons (SP-class) from a set of segments (psp in spatstat)?
 

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  1. POHow to get a SpatialPolygons (SP-class) from a set of segments (psp in spatstat)?
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    <p>I have a set of random segments drawing a kind of tessellation (of triangles, rectangles ...) in a <a href="https://stackoverflow.com/questions/14362127/how-to-generate-a-list-of-segments-from-a-list-of-random-self-intercepting-lines">window</a> (in spatstat R). I need to convert it into a set of polygons (SpatialPolygons) to calculate some indices (like area, shape indices ...).</p> <p>This is apparently simple but I couldn't find how to do it ...</p> <p>Here is a bit of code from <a href="https://stackoverflow.com/questions/14362127/how-to-generate-a-list-of-segments-from-a-list-of-random-self-intercepting-lines">Carl Witthoft</a> that generate a random pattern of self-intercepting segments :</p> <pre><code>ranpoly &lt;- function(numsegs=10,plotit=TRUE) { require(spatstat) # temp fix: put the first seg into segset. Later make it a constrained random. segset&lt;-psp(c(0,1,1,0,.25),c(0,0,1,1,0),c(1,1,0,0,1),c(0,1,1,0,.75),owin(c(0,1),c(0,1)) ) #frame the frame for (jj in 1: numsegs) { # randomly select a segment to start from, a point on the seg, the slope,and direction # later... watch for slopes that immediately exit the frame endx &lt;-sample(c(-0.2,1.2),1) #force 'x1' outside the frame # watch that sample() gotcha if(segset$n&lt;=5) sampset &lt;- c(5,5) else sampset&lt;-5:segset$n startseg&lt;-sample(sampset,1) #don't select a frame segment # this is slope of segment to be constructed slope &lt;- tan(runif(1)*2*pi-pi) # range +/- Inf # get length of selected segment seglen&lt;-lengths.psp(segset)[startseg] startcut &lt;- runif(1) # grab the coords of starting point (similar triangles) startx&lt;- segset$ends$x0[startseg] + (segset$ends$x1[startseg]-segset$ends$x0[startseg])*startcut #seglen starty&lt;- segset$ends$y0[startseg] + (segset$ends$y1[startseg]-segset$ends$y0[startseg])*startcut #seglen # make a psp object with that startpoint and slope; will adjust it after finding intersections endy &lt;- starty + slope*(endx-startx) newpsp&lt;-psp(startx,starty,endx,endy,segset$window,check=FALSE) # don't calc crossing for current element of segset hits &lt;- crossing.psp(segset[-startseg],newpsp) segdist &lt;- dist(cbind(c(startx,hits$x),c(starty,hits$y))) # dig back to get the crosspoint desired -- have to get matrixlike object out of class "dist" object # And, as.matrix puts a zero in location 1,1 kill that row. cutx &lt;- hits$x[ which.min( as.matrix(segdist)[-1,1] )] cuty &lt;- hits$y[which.min(as.matrix(segdist)[-1,1] )] segset &lt;- superimpose(segset,psp(startx,starty,cutx,cuty,segset$window)) } #end jj loop if(plotit) plot(segset,col=rainbow(numsegs)) return(invisible(segset)) } segset=ranpoly() </code></pre> <p>segset is the psp object from wich I need to create a SpatialPolygons object.</p>
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    1. USCommunity
    1. USYo B.
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      1. POHow to get a SpatialPolygons (SP-class) from a set of segments (psp in spatstat)?
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    1. COI down voted you because you question is very unclear. Your response to the first answer suddenly mentions "extracting polygons from self-intercepting segments". This is a very different question then first presented. To receive an answer to your question I would clarify it and provide code that generated the data and what you have already tried.
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      1. POHow to get a SpatialPolygons (SP-class) from a set of segments (psp in spatstat)?
      1. USJeffrey Evans
    2. COBecause you modified your post to provide example code, I removed your down vote.
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      1. POHow to get a SpatialPolygons (SP-class) from a set of segments (psp in spatstat)?
      1. USJeffrey Evans
 

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