Hi All,<br>Thanks for the tips! Just another thing, when I compute the "transition 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 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><div class="gmail_quote">On Mon, Oct 29, 2012 at 3:03 PM, Stephen Woodbridge <span dir="ltr"><<a href="mailto:woodbri@swoodbridge.com" target="_blank">woodbri@swoodbridge.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi Ed,<br>
<br>
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.<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<div class="im"><br>
<br>
<br>
On 10/29/2012 6:57 AM, Ed Linde wrote:<br>
</div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im">
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" target="_blank">nicolas.ribot@gmail.com</a><br></div><div class="im">
<mailto:<a href="mailto:nicolas.ribot@gmail.com" target="_blank">nicolas.ribot@gmail.<u></u>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" target="_blank">edolinde@gmail.com</a><br></div><div><div class="h5">
<mailto:<a href="mailto:edolinde@gmail.com" target="_blank">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" target="_blank">mwtoews@gmail.com</a><br></div></div><div class="im">
<mailto:<a href="mailto:mwtoews@gmail.com" target="_blank">mwtoews@gmail.com</a>>> wrote:<br>
>><br>
>> On 29 October 2012 21:33, Ed Linde <<a href="mailto:edolinde@gmail.com" target="_blank">edolinde@gmail.com</a><br></div><div class="im">
<mailto:<a href="mailto:edolinde@gmail.com" target="_blank">edolinde@gmail.com</a>>> wrote:<br>
>> > Hi All,<br>
>> > I need help with 2 hard problems. I store triangles in a table 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 elements.<br>
>> You can use ST_Relate with pattern 'FF2F11212' to pick out 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></div>
>> WHERE <a href="http://e.id" target="_blank">e.id</a> <<a href="http://e.id" target="_blank">http://e.id</a>> = 567 AND<div class="im"><br>
>> ST_Relate(elements.geom, e.geom, 'FF2F11212');<br>
>><br>
>> I'm not certain about your second question.<br>
>><br>
>> -Mike<br>
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