Yes, it looks like some points were not put in the right order before building a polygon, thus these "butterfly" polygons you generated. If the formed polygon are expected to be convex, you could use st_convexhull on the point cloud to generate the polygons.
On 29 October 2012 16:09, Ed Linde <edoli...@gmail.com> wrote: > Thanks Nicolas! Will look at the script that generated the polygon text.. > must have goofed something up there. > > > On Mon, Oct 29, 2012 at 4:05 PM, Nicolas Ribot <nicolas.ri...@gmail.com> > wrote: >> >> Hi, >> >> No. this is because some of your polygons are not valid: >> for instance: >> select st_isvalid('POLYGON ((593921 5219610 803,593921 5219610 >> 818,593921 5219620 818,593921 5219620 803,593921 5219610 >> 803))'::geometry); >> NOTICE: Too few points in geometry component at or near point 593921 >> 5219610 803 >> st_isvalid >> ------------ >> f >> (1 row) >> >> you can control this with st_isvalid, st_isvalidReason and correct >> them with st_makeValid. >> >> Use only valid objects before processing them with Postgis functions. >> >> Nicolas >> >> On 29 October 2012 16:03, Ed Linde <edoli...@gmail.com> wrote: >> > Thanks Nicolas. Just about the error, is this because the line segments >> > are >> > too close >> > and postgis 2.0 could not handle this? If so is there a workaround, even >> > if >> > it means >> > slightly having to "perturb" each point's position to not run into this >> > bug. >> > I was really hoping that the intersection of two polygonal shapes in 3D >> > would be fairly >> > simple in postgis 2.0 :( >> > >> > Ed >> > >> > >> > On Mon, Oct 29, 2012 at 4:00 PM, Nicolas Ribot <nicolas.ri...@gmail.com> >> > wrote: >> >> >> >> 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 >> > >> > >> > >> > _______________________________________________ >> > 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