Ok thanks, will look into that function. Because I wonder if the s/w I am using is <br>actually outputting the vertices of each face in a cyclical fashion or just <br>arbitrarily.<br><br>Cheers,<br>Ed<br><br><div class="gmail_quote">
On Mon, Oct 29, 2012 at 4:23 PM, Nicolas Ribot <span dir="ltr"><<a href="mailto:nicolas.ribot@gmail.com" target="_blank">nicolas.ribot@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Yes, it looks like some points were not put in the right order before<br>
building a polygon, thus these "butterfly" polygons you generated.<br>
If the formed polygon are expected to be convex, you could use<br>
st_convexhull on the point cloud to generate the polygons.<br>
<div class="HOEnZb"><div class="h5"><br>
On 29 October 2012 16:09, Ed Linde <<a href="mailto:edolinde@gmail.com">edolinde@gmail.com</a>> wrote:<br>
> Thanks Nicolas! Will look at the script that generated the polygon text..<br>
> must have goofed something up there.<br>
><br>
><br>
> On Mon, Oct 29, 2012 at 4:05 PM, Nicolas Ribot <<a href="mailto:nicolas.ribot@gmail.com">nicolas.ribot@gmail.com</a>><br>
> wrote:<br>
>><br>
>> Hi,<br>
>><br>
>> No. this is because some of your polygons are not valid:<br>
>> for instance:<br>
>> select st_isvalid('POLYGON ((593921 5219610 803,593921 5219610<br>
>> 818,593921 5219620 818,593921 5219620 803,593921 5219610<br>
>> 803))'::geometry);<br>
>> NOTICE: Too few points in geometry component at or near point 593921<br>
>> 5219610 803<br>
>> st_isvalid<br>
>> ------------<br>
>> f<br>
>> (1 row)<br>
>><br>
>> you can control this with st_isvalid, st_isvalidReason and correct<br>
>> them with st_makeValid.<br>
>><br>
>> Use only valid objects before processing them with Postgis functions.<br>
>><br>
>> Nicolas<br>
>><br>
>> On 29 October 2012 16:03, Ed Linde <<a href="mailto:edolinde@gmail.com">edolinde@gmail.com</a>> wrote:<br>
>> > Thanks Nicolas. Just about the error, is this because the line segments<br>
>> > are<br>
>> > too close<br>
>> > and postgis 2.0 could not handle this? If so is there a workaround, even<br>
>> > if<br>
>> > it means<br>
>> > slightly having to "perturb" each point's position to not run into this<br>
>> > bug.<br>
>> > I was really hoping that the intersection of two polygonal shapes in 3D<br>
>> > would be fairly<br>
>> > simple in postgis 2.0 :(<br>
>> ><br>
>> > Ed<br>
>> ><br>
>> ><br>
>> > On Mon, Oct 29, 2012 at 4:00 PM, Nicolas Ribot <<a href="mailto:nicolas.ribot@gmail.com">nicolas.ribot@gmail.com</a>><br>
>> > wrote:<br>
>> >><br>
>> >> If the points are computed in the right order, you can store them and<br>
>> >> pass them to st_makeLine and st_makePolygon.<br>
>> >> If not, you can form a segment between 2 closest points and connect it<br>
>> >> to the closest points.<br>
>> >><br>
>> >> On 29 October 2012 15:37, Ed Linde <<a href="mailto:edolinde@gmail.com">edolinde@gmail.com</a>> wrote:<br>
>> >> > Hi All,<br>
>> >> > Thanks for the tips! Just another thing, when I compute the<br>
>> >> > "transition<br>
>> >> > points" on each edge (shown as red points in my pdf).<br>
>> >> > I need to join them to make a polygon. Wondering how I can connect<br>
>> >> > them<br>
>> >> > together so that I start with a point and end on it<br>
>> >> > to form a closed polygon?<br>
>> >> ><br>
>> >> > Cheers,<br>
>> >> > Ed<br>
>> >> ><br>
>> >> ><br>
>> >> > On Mon, Oct 29, 2012 at 3:03 PM, Stephen Woodbridge<br>
>> >> > <<a href="mailto:woodbri@swoodbridge.com">woodbri@swoodbridge.com</a>> wrote:<br>
>> >> >><br>
>> >> >> Hi Ed,<br>
>> >> >><br>
>> >> >> Well if clarifies one thing at least, you can ignore Mike's<br>
>> >> >> st_Relate<br>
>> >> >> because 5 is not adjacent to a linear edge, it is only adjacent to a<br>
>> >> >> vertex,<br>
>> >> >> so st_touches should work fine.<br>
>> >> >><br>
>> >> >> so you are looking for:<br>
>> >> >><br>
>> >> >> 1. a specific triangle by id<br>
>> >> >> 2. that intersects triangle VC<br>
>> >> >> 3. and the triangles adjacent to triangle by id<br>
>> >> >> 4. and those that are contained in VC<br>
>> >> >> 5. sorted by distance to P1 limit 1<br>
>> >> >><br>
>> >> >> so something like:<br>
>> >> >><br>
>> >> >> select id, the_geom<br>
>> >> >> from (select id, the_geom as adjacent<br>
>> >> >> from triangles<br>
>> >> >> where st_touches(the_geom,<br>
>> >> >> (select the_geom<br>
>> >> >> from triangles a,<br>
>> >> >> (select the_geom as vc<br>
>> >> >> from vc_table<br>
>> >> >> where id='p1') b<br>
>> >> >> where <a href="http://a.id" target="_blank">a.id</a>=4)) c<br>
>> >> >> order by st_distance(c.the_geom, (select the_geom<br>
>> >> >> from points<br>
>> >> >> where id='p1')) asc limit 1;<br>
>> >> >><br>
>> >> >> Untested, but should give you a model to work with.<br>
>> >> >><br>
>> >> >> -Steve W<br>
>> >> >><br>
>> >> >><br>
>> >> >><br>
>> >> >> On 10/29/2012 6:57 AM, Ed Linde wrote:<br>
>> >> >>><br>
>> >> >>> Attached is a figure. Where the dotted line is the boundary of the<br>
>> >> >>> voronoi cell whose<br>
>> >> >>> generator is point P1. So triangle "4" intersects with the voronoi<br>
>> >> >>> boundary, but we are<br>
>> >> >>> interested in the adjacent triangles of triangle 4, which are<br>
>> >> >>> closer<br>
>> >> >>> to<br>
>> >> >>> point P1.<br>
>> >> >>> For example, triangle 5.<br>
>> >> >>><br>
>> >> >>> Hope this helps.<br>
>> >> >>> Cheers,<br>
>> >> >>> Ed<br>
>> >> >>><br>
>> >> >>> On Mon, Oct 29, 2012 at 11:50 AM, Nicolas Ribot<br>
>> >> >>> <<a href="mailto:nicolas.ribot@gmail.com">nicolas.ribot@gmail.com</a><br>
>> >> >>> <mailto:<a href="mailto:nicolas.ribot@gmail.com">nicolas.ribot@gmail.com</a>>> wrote:<br>
>> >> >>><br>
>> >> >>> Could you draw a figure ?<br>
>> >> >>><br>
>> >> >>> Nicolas<br>
>> >> >>><br>
>> >> >>> On 29 October 2012 11:03, Ed Linde <<a href="mailto:edolinde@gmail.com">edolinde@gmail.com</a><br>
>> >> >>> <mailto:<a href="mailto:edolinde@gmail.com">edolinde@gmail.com</a>>> wrote:<br>
>> >> >>> > Hi All,<br>
>> >> >>> > Thanks for the suggestions.<br>
>> >> >>> > For 1) I will look into how ST_touches works and see if it<br>
>> >> >>> can<br>
>> >> >>> pick up all<br>
>> >> >>> > the adjacent polygons to<br>
>> >> >>> > the one I have. And also look into Mike's suggestion on<br>
>> >> >>> ST_relate...though I<br>
>> >> >>> > must admit it looks<br>
>> >> >>> > more complex.<br>
>> >> >>> > For 2) I will try to clarify it a bit more... its harder to<br>
>> >> >>> do<br>
>> >> >>> without a<br>
>> >> >>> > figure :) but here goes.<br>
>> >> >>> ><br>
>> >> >>> > Lets say we have a point Q which is the generator of a<br>
>> >> >>> voronoi<br>
>> >> >>> cell. Now I<br>
>> >> >>> > compute the<br>
>> >> >>> > intersection between the voronoi cell boundaries and my<br>
>> >> >>> triangulation (Set<br>
>> >> >>> > of polygons)<br>
>> >> >>> > using ST_intersect. Once I have these triangles.. I say pick<br>
>> >> >>> one<br>
>> >> >>> triangle T<br>
>> >> >>> > that is<br>
>> >> >>> > intersecting the voronoi cell boundary of Q.<br>
>> >> >>> > For all the triangles adjacent to T, I need to know which<br>
>> >> >>> triangles are<br>
>> >> >>> > INSIDE the voronoi<br>
>> >> >>> > boundary (closer to Q) and which adjacent triangles are just<br>
>> >> >>> OUTSIDE the<br>
>> >> >>> > voronoi<br>
>> >> >>> > boundary (farther from Q). I am basically testing for a<br>
>> >> >>> certain<br>
>> >> >>> property by<br>
>> >> >>> > "shrinking" the<br>
>> >> >>> > voronoi cell (closer to Q) and another property when<br>
>> >> >>> "expanding"<br>
>> >> >>> the voronoi<br>
>> >> >>> > cell (away from Q).<br>
>> >> >>> > Just need to make this division of triangles. Haven't<br>
>> >> >>> thought<br>
>> >> >>> of<br>
>> >> >>> a nice way<br>
>> >> >>> > to do this in postgis 2.0<br>
>> >> >>> > So any suggestions would greatly help.<br>
>> >> >>> ><br>
>> >> >>> > Thanks,<br>
>> >> >>> > Ed<br>
>> >> >>> ><br>
>> >> >>> > On Mon, Oct 29, 2012 at 10:15 AM, Mike Toews<br>
>> >> >>> <<a href="mailto:mwtoews@gmail.com">mwtoews@gmail.com</a><br>
>> >> >>> <mailto:<a href="mailto:mwtoews@gmail.com">mwtoews@gmail.com</a>>> wrote:<br>
>> >> >>> >><br>
>> >> >>> >> On 29 October 2012 21:33, Ed Linde <<a href="mailto:edolinde@gmail.com">edolinde@gmail.com</a><br>
>> >> >>> <mailto:<a href="mailto:edolinde@gmail.com">edolinde@gmail.com</a>>> wrote:<br>
>> >> >>> >> > Hi All,<br>
>> >> >>> >> > I need help with 2 hard problems. I store triangles in a<br>
>> >> >>> table<br>
>> >> >>> as<br>
>> >> >>> >> > POLYGON.<br>
>> >> >>> >> ><br>
>> >> >>> >> > 1. I want to know for a given triangle, which triangles<br>
>> >> >>> share<br>
>> >> >>> an edge<br>
>> >> >>> >> > (adjacent) with this triangle.<br>
>> >> >>> >><br>
>> >> >>> >> Sounds like you have a finite element mesh with nodes and<br>
>> >> >>> elements.<br>
>> >> >>> >> You can use ST_Relate with pattern 'FF2F11212' to pick out<br>
>> >> >>> elements<br>
>> >> >>> >> that share the same edge. This DE-9-IM is sort-of a custom<br>
>> >> >>> ST_Touches,<br>
>> >> >>> >> but only takes linear boundary overlaps. So if you have a<br>
>> >> >>> table<br>
>> >> >>> >> "elements", and you want to find ones that touch ID 567:<br>
>> >> >>> >><br>
>> >> >>> >> SELECT elements.*<br>
>> >> >>> >> FROM elements, elements as e<br>
>> >> >>> >> WHERE <a href="http://e.id" target="_blank">e.id</a> <<a href="http://e.id" target="_blank">http://e.id</a>> = 567 AND<br>
>> >> >>><br>
>> >> >>> >> ST_Relate(elements.geom, e.geom, 'FF2F11212');<br>
>> >> >>> >><br>
>> >> >>> >> I'm not certain about your second question.<br>
>> >> >>> >><br>
>> >> >>> >> -Mike<br>
>> >> >>> >> _______________________________________________<br>
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</div></div></blockquote></div><br>