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