[postgis-users] Difficult Problem with Polygons
Ed Linde
edolinde at gmail.com
Mon Oct 29 08:09:23 PDT 2012
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.ribot at 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 <edolinde at 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.ribot at 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 <edolinde at 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
> >> > <woodbri at 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.ribot at gmail.com
> >> >>> <mailto:nicolas.ribot at gmail.com>> wrote:
> >> >>>
> >> >>> Could you draw a figure ?
> >> >>>
> >> >>> Nicolas
> >> >>>
> >> >>> On 29 October 2012 11:03, Ed Linde <edolinde at gmail.com
> >> >>> <mailto:edolinde at 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 <
> mwtoews at gmail.com
> >> >>> <mailto:mwtoews at gmail.com>> wrote:
> >> >>> >>
> >> >>> >> On 29 October 2012 21:33, Ed Linde <edolinde at gmail.com
> >> >>> <mailto:edolinde at 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 at postgis.refractions.net
> >> >>> <mailto:postgis-users at postgis.refractions.net>
> >> >>>
> >> >>> >>
> http://postgis.refractions.net/mailman/listinfo/postgis-users
> >> >>> >
> >> >>> >
> >> >>> >
> >> >>> > _______________________________________________
> >> >>> > postgis-users mailing list
> >> >>> > postgis-users at postgis.refractions.net
> >> >>> <mailto:postgis-users at postgis.refractions.net>
> >> >>>
> >> >>> >
> http://postgis.refractions.net/mailman/listinfo/postgis-users
> >> >>> >
> >> >>> _______________________________________________
> >> >>> postgis-users mailing list
> >> >>> postgis-users at postgis.refractions.net
> >> >>> <mailto:postgis-users at postgis.refractions.net>
> >> >>>
> >> >>> http://postgis.refractions.net/mailman/listinfo/postgis-users
> >> >>>
> >> >>>
> >> >>>
> >> >>>
> >> >>> _______________________________________________
> >> >>> postgis-users mailing list
> >> >>> postgis-users at postgis.refractions.net
> >> >>> http://postgis.refractions.net/mailman/listinfo/postgis-users
> >> >>>
> >> >>
> >> >> _______________________________________________
> >> >> postgis-users mailing list
> >> >> postgis-users at postgis.refractions.net
> >> >> http://postgis.refractions.net/mailman/listinfo/postgis-users
> >> >
> >> >
> >> >
> >> > _______________________________________________
> >> > postgis-users mailing list
> >> > postgis-users at postgis.refractions.net
> >> > http://postgis.refractions.net/mailman/listinfo/postgis-users
> >> >
> >> _______________________________________________
> >> postgis-users mailing list
> >> postgis-users at postgis.refractions.net
> >> http://postgis.refractions.net/mailman/listinfo/postgis-users
> >
> >
> >
> > _______________________________________________
> > postgis-users mailing list
> > postgis-users at postgis.refractions.net
> > http://postgis.refractions.net/mailman/listinfo/postgis-users
> >
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/postgis-users/attachments/20121029/4c34317e/attachment.html>
More information about the postgis-users
mailing list