Hi All, Wondering if that diagram made things any simpler or is it still not clear what the problem is?
Thanks, Ed On Mon, Oct 29, 2012 at 11:57 AM, Ed Linde <edoli...@gmail.com> wrote: > Attached is a figure. Where the dotted line is the boundary of the voronoi > cell whose > generator is point P1. So triangle "4" intersects with the voronoi > boundary, but we are > interested in the adjacent triangles of triangle 4, which are closer to > point P1. > For example, triangle 5. > > Hope this helps. > Cheers, > Ed > > > On Mon, Oct 29, 2012 at 11:50 AM, Nicolas Ribot > <nicolas.ri...@gmail.com>wrote: > >> Could you draw a figure ? >> >> Nicolas >> >> On 29 October 2012 11:03, Ed Linde <edoli...@gmail.com> wrote: >> > Hi All, >> > Thanks for the suggestions. >> > For 1) I will look into how ST_touches works and see if it can pick up >> all >> > the adjacent polygons to >> > the one I have. And also look into Mike's suggestion on >> ST_relate...though I >> > must admit it looks >> > more complex. >> > For 2) I will try to clarify it a bit more... its harder to do without a >> > figure :) but here goes. >> > >> > Lets say we have a point Q which is the generator of a voronoi cell. >> Now I >> > compute the >> > intersection between the voronoi cell boundaries and my triangulation >> (Set >> > of polygons) >> > using ST_intersect. Once I have these triangles.. I say pick one >> triangle T >> > that is >> > intersecting the voronoi cell boundary of Q. >> > For all the triangles adjacent to T, I need to know which triangles are >> > INSIDE the voronoi >> > boundary (closer to Q) and which adjacent triangles are just OUTSIDE the >> > voronoi >> > boundary (farther from Q). I am basically testing for a certain >> property by >> > "shrinking" the >> > voronoi cell (closer to Q) and another property when "expanding" the >> voronoi >> > cell (away from Q). >> > Just need to make this division of triangles. Haven't thought of a nice >> way >> > to do this in postgis 2.0 >> > So any suggestions would greatly help. >> > >> > Thanks, >> > Ed >> > >> > On Mon, Oct 29, 2012 at 10:15 AM, Mike Toews <mwto...@gmail.com> wrote: >> >> >> >> On 29 October 2012 21:33, Ed Linde <edoli...@gmail.com> wrote: >> >> > Hi All, >> >> > I need help with 2 hard problems. I store triangles in a table as >> >> > POLYGON. >> >> > >> >> > 1. I want to know for a given triangle, which triangles share an edge >> >> > (adjacent) with this triangle. >> >> >> >> Sounds like you have a finite element mesh with nodes and elements. >> >> You can use ST_Relate with pattern 'FF2F11212' to pick out elements >> >> that share the same edge. This DE-9-IM is sort-of a custom ST_Touches, >> >> but only takes linear boundary overlaps. So if you have a table >> >> "elements", and you want to find ones that touch ID 567: >> >> >> >> SELECT elements.* >> >> FROM elements, elements as e >> >> WHERE e.id = 567 AND >> >> ST_Relate(elements.geom, e.geom, 'FF2F11212'); >> >> >> >> I'm not certain about your second question. >> >> >> >> -Mike >> >> _______________________________________________ >> >> postgis-users mailing list >> >> postgis-users@postgis.refractions.net >> >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> > >> > >> > >> > _______________________________________________ >> > postgis-users mailing list >> > postgis-users@postgis.refractions.net >> > http://postgis.refractions.net/mailman/listinfo/postgis-users >> > >> _______________________________________________ >> postgis-users mailing list >> postgis-users@postgis.refractions.net >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> > >
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