I tried something like the following without removing the same points ad it seems to work:<br><br>SELECT st_astext(ST_ConvexHull(ST_GeomFromText('MULTIPOINT(593901 5219610 814,593901 5219610 814,593899 5219610 814,593899 5219610 814,593901 5219610 814)'))); <br>
"LINESTRING Z (593901 5219610 814,593899 5219610 814)"<br><br>Ed<br><br><div class="gmail_quote">On Mon, Oct 29, 2012 at 5:23 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">You should filter out the consecutive points. If there are more than 2<br>
points, you can then call st_convexHull() on the point set:<br>
<br>
with points as (<br>
select 'POINT (0 0)'::geometry as geom<br>
UNION<br>
select 'POINT (1 0)'::geometry as geom<br>
UNION<br>
select 'POINT (1 1)'::geometry as geom<br>
) select st_convexHull(st_collect(geom))<br>
from points;<br>
<br>
If the points are aligned, convexHull will be a linestring, that you<br>
can discard or further process according to your needs.<br>
<span class="HOEnZb"><font color="#888888"><br>
Nicolas<br>
</font></span><div class="HOEnZb"><div class="h5"><br>
On 29 October 2012 16:51, Ed Linde <<a href="mailto:edolinde@gmail.com">edolinde@gmail.com</a>> wrote:<br>
> Hi Nicolas,<br>
> It seems like sometimes the points are one and the same and I get<br>
> linestrings and not<br>
> actual polygons. I pass these points in from a perl script, so is there a<br>
> way I can just<br>
> give the raw x,y,z coordinates of these points and do a st_convexhull<br>
> function on them?<br>
> Could you please give me a small example?<br>
><br>
> I tried something like:<br>
> The two coordinates marked in red and marked in orange are the same.<br>
><br>
> bounds=# insert into vfaces values (1,<br>
> bounds(# ST_GeomFromText('POLYGON((593901 5219610 814,593901 5219610<br>
> 814,593899 5219610 814,593899 5219610 814,593901 5219610 814))') );<br>
> INSERT 0 1<br>
> bounds=# select st_isvalid(geomtext) from vfaces;<br>
> NOTICE: Too few points in geometry component at or near point 593901<br>
> 5219610 814<br>
><br>
> st_isvalid<br>
> ------------<br>
> f<br>
> (1 row)<br>
><br>
> Thanks,<br>
> Ed<br>
><br>
><br>
><br>
><br>
> On Mon, Oct 29, 2012 at 4:26 PM, Ed Linde <<a href="mailto:edolinde@gmail.com">edolinde@gmail.com</a>> wrote:<br>
>><br>
>> Ok thanks, will look into that function. Because I wonder if the s/w I am<br>
>> using is<br>
>> actually outputting the vertices of each face in a cyclical fashion or<br>
>> just<br>
>> arbitrarily.<br>
>><br>
>> Cheers,<br>
>> Ed<br>
>><br>
>><br>
>> On Mon, Oct 29, 2012 at 4:23 PM, Nicolas Ribot <<a href="mailto:nicolas.ribot@gmail.com">nicolas.ribot@gmail.com</a>><br>
>> wrote:<br>
>>><br>
>>> 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>
>>><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<br>
>>> > text..<br>
>>> > must have goofed something up there.<br>
>>> ><br>
>>> ><br>
>>> > On Mon, Oct 29, 2012 at 4:05 PM, Nicolas Ribot<br>
>>> > <<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<br>
>>> >> > segments<br>
>>> >> > are<br>
>>> >> > too close<br>
>>> >> > and postgis 2.0 could not handle this? If so is there a workaround,<br>
>>> >> > even<br>
>>> >> > if<br>
>>> >> > it means<br>
>>> >> > slightly having to "perturb" each point's position to not run into<br>
>>> >> > this<br>
>>> >> > bug.<br>
>>> >> > I was really hoping that the intersection of two polygonal shapes in<br>
>>> >> > 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<br>
>>> >> > <<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<br>
>>> >> >> and<br>
>>> >> >> pass them to st_makeLine and st_makePolygon.<br>
>>> >> >> If not, you can form a segment between 2 closest points and connect<br>
>>> >> >> 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<br>
>>> >> >> > 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<br>
>>> >> >> >> 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<br>
>>> >> >> >>> the<br>
>>> >> >> >>> voronoi cell whose<br>
>>> >> >> >>> generator is point P1. So triangle "4" intersects with the<br>
>>> >> >> >>> 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<br>
>>> >> >> >>> 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<br>
>>> >> >> >>> 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<br>
>>> >> >> >>> 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<br>
>>> >> >> >>> which<br>
>>> >> >> >>> triangles are<br>
>>> >> >> >>> > INSIDE the voronoi<br>
>>> >> >> >>> > boundary (closer to Q) and which adjacent triangles are<br>
>>> >> >> >>> 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<br>
>>> >> >> >>> in a<br>
>>> >> >> >>> table<br>
>>> >> >> >>> as<br>
>>> >> >> >>> >> > POLYGON.<br>
>>> >> >> >>> >> ><br>
>>> >> >> >>> >> > 1. I want to know for a given triangle, which<br>
>>> >> >> >>> triangles<br>
>>> >> >> >>> share<br>
>>> >> >> >>> an edge<br>
>>> >> >> >>> >> > (adjacent) with this triangle.<br>
>>> >> >> >>> >><br>
>>> >> >> >>> >> Sounds like you have a finite element mesh with nodes<br>
>>> >> >> >>> and<br>
>>> >> >> >>> elements.<br>
>>> >> >> >>> >> You can use ST_Relate with pattern 'FF2F11212' to pick<br>
>>> >> >> >>> out<br>
>>> >> >> >>> elements<br>
>>> >> >> >>> >> that share the same edge. This DE-9-IM is sort-of a<br>
>>> >> >> >>> custom<br>
>>> >> >> >>> ST_Touches,<br>
>>> >> >> >>> >> but only takes linear boundary overlaps. So if you have<br>
>>> >> >> >>> a<br>
>>> >> >> >>> table<br>
>>> >> >> >>> >> "elements", and you want to find ones that touch ID<br>
>>> >> >> >>> 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>
>>> >> >> >>> >><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>
>>> >> >> >>> ><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>
>>> >> >> >>><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>
>>> >> ><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>
>>> ><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>
>><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>