If the points are computed in the right order, you can store them and pass them to st_makeLine and st_makePolygon. If not, you can form a segment between 2 closest points and connect it to the closest points.
On 29 October 2012 15:37, Ed Linde <edoli...@gmail.com> wrote: > Hi All, > Thanks for the tips! Just another thing, when I compute the "transition > points" on each edge (shown as red points in my pdf). > I need to join them to make a polygon. Wondering how I can connect them > together so that I start with a point and end on it > to form a closed polygon? > > Cheers, > Ed > > > On Mon, Oct 29, 2012 at 3:03 PM, Stephen Woodbridge > <wood...@swoodbridge.com> wrote: >> >> Hi Ed, >> >> Well if clarifies one thing at least, you can ignore Mike's st_Relate >> because 5 is not adjacent to a linear edge, it is only adjacent to a vertex, >> so st_touches should work fine. >> >> so you are looking for: >> >> 1. a specific triangle by id >> 2. that intersects triangle VC >> 3. and the triangles adjacent to triangle by id >> 4. and those that are contained in VC >> 5. sorted by distance to P1 limit 1 >> >> so something like: >> >> select id, the_geom >> from (select id, the_geom as adjacent >> from triangles >> where st_touches(the_geom, >> (select the_geom >> from triangles a, >> (select the_geom as vc >> from vc_table >> where id='p1') b >> where a.id=4)) c >> order by st_distance(c.the_geom, (select the_geom >> from points >> where id='p1')) asc limit 1; >> >> Untested, but should give you a model to work with. >> >> -Steve W >> >> >> >> On 10/29/2012 6:57 AM, Ed Linde 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 >>> <mailto:nicolas.ri...@gmail.com>> wrote: >>> >>> Could you draw a figure ? >>> >>> Nicolas >>> >>> On 29 October 2012 11:03, Ed Linde <edoli...@gmail.com >>> <mailto: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 >>> <mailto:mwto...@gmail.com>> wrote: >>> >> >>> >> On 29 October 2012 21:33, Ed Linde <edoli...@gmail.com >>> <mailto: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 <http://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 >>> <mailto:postgis-users@postgis.refractions.net> >>> >>> >> http://postgis.refractions.net/mailman/listinfo/postgis-users >>> > >>> > >>> > >>> > _______________________________________________ >>> > postgis-users mailing list >>> > postgis-users@postgis.refractions.net >>> <mailto:postgis-users@postgis.refractions.net> >>> >>> > http://postgis.refractions.net/mailman/listinfo/postgis-users >>> > >>> _______________________________________________ >>> postgis-users mailing list >>> postgis-users@postgis.refractions.net >>> <mailto: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 > > > > _______________________________________________ > 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