Thanks Nicolas. Just about the error, is this because the line segments are too close <br>and postgis 2.0 could not handle this? If so is there a workaround, even if it means <br>slightly having to "perturb" each point's position to not run into this bug.<br>
I was really hoping that the intersection of two polygonal shapes in 3D would be fairly <br>simple in postgis 2.0 :(<br><br>Ed<br><br><div class="gmail_quote">On Mon, Oct 29, 2012 at 4:00 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">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>
<div class="HOEnZb"><div class="h5"><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 "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 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 st_Relate<br>
>> because 5 is not adjacent to a linear edge, it is only adjacent to a 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 closer 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 <<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 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 do<br>
>>> without a<br>
>>> > figure :) but here goes.<br>
>>> ><br>
>>> > Lets say we have a point Q which is the generator of a 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 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 certain<br>
>>> property by<br>
>>> > "shrinking" the<br>
>>> > voronoi cell (closer to Q) and another property when "expanding"<br>
>>> the voronoi<br>
>>> > cell (away from Q).<br>
>>> > Just need to make this division of triangles. Haven't thought 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 <<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 table<br>
>>> as<br>
>>> >> > POLYGON.<br>
>>> >> ><br>
>>> >> > 1. I want to know for a given triangle, which triangles 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 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>
>>> >> postgis-users mailing list<br>
>>> >> <a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>
>>> <mailto:<a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a>><br>
>>><br>
>>> >> <a href="http://postgis.refractions.net/mailman/listinfo/postgis-users" target="_blank">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><br>
>>> ><br>
>>> ><br>
>>> ><br>
>>> > _______________________________________________<br>
>>> > postgis-users mailing list<br>
>>> > <a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>
>>> <mailto:<a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a>><br>
>>><br>
>>> > <a href="http://postgis.refractions.net/mailman/listinfo/postgis-users" target="_blank">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><br>
>>> ><br>
>>> _______________________________________________<br>
>>> postgis-users mailing list<br>
>>> <a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>
>>> <mailto:<a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a>><br>
>>><br>
>>> <a href="http://postgis.refractions.net/mailman/listinfo/postgis-users" target="_blank">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><br>
>>><br>
>>><br>
>>><br>
>>><br>
>>> _______________________________________________<br>
>>> postgis-users mailing list<br>
>>> <a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>
>>> <a href="http://postgis.refractions.net/mailman/listinfo/postgis-users" target="_blank">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><br>
>>><br>
>><br>
>> _______________________________________________<br>
>> postgis-users mailing list<br>
>> <a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>
>> <a href="http://postgis.refractions.net/mailman/listinfo/postgis-users" target="_blank">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><br>
><br>
><br>
><br>
> _______________________________________________<br>
> postgis-users mailing list<br>
> <a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>
> <a href="http://postgis.refractions.net/mailman/listinfo/postgis-users" target="_blank">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><br>
><br>
_______________________________________________<br>
postgis-users mailing list<br>
<a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>
<a href="http://postgis.refractions.net/mailman/listinfo/postgis-users" target="_blank">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><br>
</div></div></blockquote></div><br>