Re: [postgis-users] Difficult Problem with Polygons

[Ed Linde]

I tried something like the following without removing the same points ad it
seems to work:

SELECT st_astext(ST_ConvexHull(ST_GeomFromText('MULTIPOINT(593901 5219610
814,593901 5219610 814,593899 5219610 814,593899 5219610 814,593901 5219610
814)')));
"LINESTRING Z (593901 5219610 814,593899 5219610 814)"

Ed

On Mon, Oct 29, 2012 at 5:23 PM, Nicolas Ribot wrote:

> You should filter out the consecutive points. If there are more than 2
> points, you can then call st_convexHull() on the point set:
>
> with points as (
> select 'POINT (0 0)'::geometry as geom
> UNION
> select 'POINT (1 0)'::geometry as geom
> UNION
> select 'POINT (1 1)'::geometry as geom
> ) select st_convexHull(st_collect(geom))
> from points;
>
> If the points are aligned, convexHull will be a linestring, that you
> can discard or further process according to your needs.
>
> Nicolas
>
> On 29 October 2012 16:51, Ed Linde  wrote:
> > Hi Nicolas,
> > It seems like sometimes the points are one and the same and I get
> > linestrings and not
> > actual polygons. I pass these points in from a perl script, so is there a
> > way I can just
> > give the raw x,y,z coordinates of these points and do a st_convexhull
> > function on them?
> > Could you please give me a small example?
> >
> > I tried something like:
> > The two coordinates marked in red and marked in orange are the same.
> >
> > bounds=# insert into vfaces values (1,
> > bounds(# ST_GeomFromText('POLYGON((593901 5219610 814,593901 5219610
> > 814,593899 5219610 814,593899 5219610 814,593901 5219610 814))') );
> > INSERT 0 1
> > bounds=# select st_isvalid(geomtext) from vfaces;
> > NOTICE:  Too few points in geometry component at or near point 593901
> > 5219610 814
> >
> >  st_isvalid
> > 
> >  f
> > (1 row)
> >
> > Thanks,
> > Ed
> >
> >
> >
> >
> > On Mon, Oct 29, 2012 at 4:26 PM, Ed Linde  wrote:
> >>
> >> Ok thanks, will look into that function. Because I wonder if the s/w I
> am
> >> using is
> >> actually outputting the vertices of each face in a cyclical fashion or
> >> just
> >> arbitrarily.
> >>
> >> Cheers,
> >> Ed
> >>
> >>
> >> On Mon, Oct 29, 2012 at 4:23 PM, Nicolas Ribot  >
> >> wrote:
> >>>
> >>> Yes, it looks like some points were not put in the right order before
> >>> building a polygon, thus these "butterfly" polygons you generated.
> >>> If the formed polygon are expected to be convex, you could use
> >>> st_convexhull on the point cloud to generate the polygons.
> >>>
> >>> On 29 October 2012 16:09, Ed Linde  wrote:
> >>> > 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
> >>> > 
> >>> > 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  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
> >>> >> > 
> >>> >> > 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  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?
> >>> >> >> >
> >>> >

Re: [postgis-users] Difficult Problem with Polygons

[Nicolas Ribot]

You should filter out the consecutive points. If there are more than 2
points, you can then call st_convexHull() on the point set:

with points as (
select 'POINT (0 0)'::geometry as geom
UNION
select 'POINT (1 0)'::geometry as geom
UNION
select 'POINT (1 1)'::geometry as geom
) select st_convexHull(st_collect(geom))
from points;

If the points are aligned, convexHull will be a linestring, that you
can discard or further process according to your needs.

Nicolas

On 29 October 2012 16:51, Ed Linde  wrote:
> Hi Nicolas,
> It seems like sometimes the points are one and the same and I get
> linestrings and not
> actual polygons. I pass these points in from a perl script, so is there a
> way I can just
> give the raw x,y,z coordinates of these points and do a st_convexhull
> function on them?
> Could you please give me a small example?
>
> I tried something like:
> The two coordinates marked in red and marked in orange are the same.
>
> bounds=# insert into vfaces values (1,
> bounds(# ST_GeomFromText('POLYGON((593901 5219610 814,593901 5219610
> 814,593899 5219610 814,593899 5219610 814,593901 5219610 814))') );
> INSERT 0 1
> bounds=# select st_isvalid(geomtext) from vfaces;
> NOTICE:  Too few points in geometry component at or near point 593901
> 5219610 814
>
>  st_isvalid
> 
>  f
> (1 row)
>
> Thanks,
> Ed
>
>
>
>
> On Mon, Oct 29, 2012 at 4:26 PM, Ed Linde  wrote:
>>
>> Ok thanks, will look into that function. Because I wonder if the s/w I am
>> using is
>> actually outputting the vertices of each face in a cyclical fashion or
>> just
>> arbitrarily.
>>
>> Cheers,
>> Ed
>>
>>
>> On Mon, Oct 29, 2012 at 4:23 PM, Nicolas Ribot 
>> wrote:
>>>
>>> Yes, it looks like some points were not put in the right order before
>>> building a polygon, thus these "butterfly" polygons you generated.
>>> If the formed polygon are expected to be convex, you could use
>>> st_convexhull on the point cloud to generate the polygons.
>>>
>>> On 29 October 2012 16:09, Ed Linde  wrote:
>>> > 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
>>> > 
>>> > 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  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
>>> >> > 
>>> >> > 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  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
>>> >> >> >  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
>>> >> >> >>

Re: [postgis-users] Difficult Problem with Polygons

[Ed Linde]

Hi Nicolas,
It seems like sometimes the points are one and the same and I get
linestrings and not
actual polygons. I pass these points in from a perl script, so is there a
way I can just
give the raw x,y,z coordinates of these points and do a st_convexhull
function on them?
Could you please give me a small example?

I tried something like:
The two coordinates marked in red and marked in orange are the same.

bounds=# insert into vfaces values (1,
bounds(# ST_GeomFromText('POLYGON((593901 5219610 814,593901 5219610 814,593899
5219610 814,593899 5219610 814,593901 5219610 814))') );
INSERT 0 1
bounds=# select st_isvalid(geomtext) from vfaces;
NOTICE:  Too few points in geometry component at or near point 593901
5219610 814
 st_isvalid

 f
(1 row)

Thanks,
Ed



On Mon, Oct 29, 2012 at 4:26 PM, Ed Linde  wrote:

> Ok thanks, will look into that function. Because I wonder if the s/w I am
> using is
> actually outputting the vertices of each face in a cyclical fashion or
> just
> arbitrarily.
>
> Cheers,
> Ed
>
>
> On Mon, Oct 29, 2012 at 4:23 PM, Nicolas Ribot wrote:
>
>> Yes, it looks like some points were not put in the right order before
>> building a polygon, thus these "butterfly" polygons you generated.
>> If the formed polygon are expected to be convex, you could use
>> st_convexhull on the point cloud to generate the polygons.
>>
>> On 29 October 2012 16:09, Ed Linde  wrote:
>> > 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 > >
>> > 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  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.ri...@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  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
>> >> >> >  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
>> >> >> >>  

Re: [postgis-users] Difficult Problem with Polygons

[Ed Linde]

Ok thanks, will look into that function. Because I wonder if the s/w I am
using is
actually outputting the vertices of each face in a cyclical fashion or just
arbitrarily.

Cheers,
Ed

On Mon, Oct 29, 2012 at 4:23 PM, Nicolas Ribot wrote:

> Yes, it looks like some points were not put in the right order before
> building a polygon, thus these "butterfly" polygons you generated.
> If the formed polygon are expected to be convex, you could use
> st_convexhull on the point cloud to generate the polygons.
>
> On 29 October 2012 16:09, Ed Linde  wrote:
> > 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 
> > 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  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.ri...@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  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
> >> >> >  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
> >> >> >>>  >> >> >>> > wrote:
> >> >> >>>
> >> >> >>> Could you draw a figure ?

Re: [postgis-users] Difficult Problem with Polygons

[Nicolas Ribot]

Yes, it looks like some points were not put in the right order before
building a polygon, thus these "butterfly" polygons you generated.
If the formed polygon are expected to be convex, you could use
st_convexhull on the point cloud to generate the polygons.

On 29 October 2012 16:09, Ed Linde  wrote:
> 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 
> 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  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 
>> > 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  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
>> >> >  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
>> >> >>> > >> >>> > wrote:
>> >> >>>
>> >> >>> Could you draw a figure ?
>> >> >>>
>> >> >>> Nicolas
>> >> >>>
>> >> >>> On 29 October 2012 11:03, Ed Linde > >> >>> > 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.
>> >> >

Re: [postgis-users] Difficult Problem with Polygons

[Ed Linde]

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 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  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 
> > 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  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
> >> >  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
> >> >>>  >> >>> > wrote:
> >> >>>
> >> >>> Could you draw a figure ?
> >> >>>
> >> >>> Nicolas
> >> >>>
> >> >>> On 29 October 2012 11:03, Ed Linde  >> >>> > 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 

Re: [postgis-users] Difficult Problem with Polygons

[Nicolas Ribot]

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  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 
> 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  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
>> >  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
>> >>> > >>> > wrote:
>> >>>
>> >>> Could you draw a figure ?
>> >>>
>> >>> Nicolas
>> >>>
>> >>> On 29 October 2012 11:03, Ed Linde > >>> > 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
>> >>>   

Re: [postgis-users] Difficult Problem with Polygons

[Ed Linde]

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 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  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
> >  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.ri...@gmail.com
> >>> > wrote:
> >>>
> >>> Could you draw a figure ?
> >>>
> >>> Nicolas
> >>>
> >>> On 29 October 2012 11:03, Ed Linde  >>> > 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  >>> > wrote:
> >>>  >>
> >>>  >> On 29 October 2012 21:33, Ed Linde  >>> > wrote:
> >>>  >> > Hi All,
> >>>  >> > I need

Re: [postgis-users] Difficult Problem with Polygons

[Nicolas Ribot]

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  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
>  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 >> > wrote:
>>>
>>> Could you draw a figure ?
>>>
>>> Nicolas
>>>
>>> On 29 October 2012 11:03, Ed Linde >> > 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 >> > wrote:
>>>  >>
>>>  >> On 29 October 2012 21:33, Ed Linde >> > 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.*
>>>  >> F

Re: [postgis-users] Difficult Problem with Polygons

[Ed Linde]

Hi All,
I was trying to do this intersection between two tables, I have inserted
the selects for the two tables and the error. Also the postgis full version
information.
Is there a way to get around this problem? Is this a bug? The polygons in
both tables contain 3D points. Could this be a problem?

Cheers,
Ed

select a.id, ST_AsText(st_intersection(a.geomtext, b.geomtext)) the_tris
from small_tris a, vfaces b
where st_intersects (a.geomtext, b.geomtext);

ERROR:  Error performing intersection: TopologyException: found non-noded
intersection between LINESTRING (593907 5.2196e+06, 593915 5.21961e+06) and
LINESTRING (593911 5.21961e+06, 593908 5.2196e+06) at 593908.598
5219602 809.899918

** Error **

ERROR: Error performing intersection: TopologyException: found non-noded
intersection between LINESTRING (593907 5.2196e+06, 593915 5.21961e+06) and
LINESTRING (593911 5.21961e+06, 593908 5.2196e+06) at 593908.598
5219602 809.899918
SQL state: XX000


 SELECT PostGIS_full_version();

postgis_full_version


---
 POSTGIS="2.0.0alpha7SVN" GEOS="3.3.2-CAPI-1.7.2" PROJ="Rel. 4.7.1, 23
September 2009" GDAL="GDAL 1.9.0, released 2011/12/29" LIBXML="2.7.8"
 USE_STATS
(1 row)


bounds=# select gen_id, ST_AsText(geomtext) from vfaces;
 gen_id |
st_astext
+-
  7 | POLYGON Z ((593908 5219600 803,593907 5219600 818,593915 5219610
818,593911 5219610 803,593908 5219600 803))
  7 | POLYGON Z ((593908 5219600 803,593899 5219600 803,593899 5219600
818,593907 5219600 818,593908 5219600 803))
  7 | POLYGON Z ((593908 5219600 803,593911 5219610 803,593903 5219620
803,593899 5219620 803,593899 5219600 803,593908 5219600 803))
  7 | POLYGON Z ((593899 5219620 803,593899 5219620 818,593899 5219600
818,593899 5219600 803,593899 5219620 803))
  7 | POLYGON Z ((593899 5219620 803,593903 5219620 803,593912 5219620
818,593899 5219620 818,593899 5219620 803))
  7 | POLYGON Z ((593912 5219620 818,593903 5219620 803,593911 5219610
803,593915 5219610 818,593912 5219620 818))
  7 | POLYGON Z ((593912 5219620 818,593915 5219610 818,593907 5219600
818,593899 5219600 818,593899 5219620 818,593912 5219620 818))
 16 | POLYGON Z ((593921 5219600 803,593921 5219610 803,593911 5219610
803,593908 5219600 803,593921 5219600 803))
 16 | POLYGON Z ((593921 5219600 803,593921 5219600 818,593921 5219610
818,593921 5219610 803,593921 5219600 803))
 16 | POLYGON Z ((593921 5219600 803,593908 5219600 803,593907 5219600
818,593921 5219600 818,593921 5219600 803))
 16 | POLYGON Z ((593911 5219610 803,593921 5219610 803,593921 5219610
818,593915 5219610 818,593911 5219610 803))
 16 | POLYGON Z ((593911 5219610 803,593915 5219610 818,593907 5219600
818,593908 5219600 803,593911 5219610 803))
 16 | POLYGON Z ((593907 5219600 818,593915 5219610 818,593921 5219610
818,593921 5219600 818,593907 5219600 818))
 18 | POLYGON Z ((593921 5219610 803,593911 5219610 803,593915 5219610
818,593921 5219610 818,593921 5219610 803))
 18 | POLYGON Z ((593921 5219610 803,593921 5219620 803,593903 5219620
803,593911 5219610 803,593921 5219610 803))
 18 | POLYGON Z ((593921 5219610 803,593921 5219610 818,593921 5219620
818,593921 5219620 803,593921 5219610 803))
 18 | POLYGON Z ((593912 5219620 818,593915 5219610 818,593911 5219610
803,593903 5219620 803,593912 5219620 818))
 18 | POLYGON Z ((593912 5219620 818,593921 5219620 818,593921 5219610
818,593915 5219610 818,593912 5219620 818))
 18 | POLYGON Z ((593912 5219620 818,593903 5219620 803,593921 5219620
803,593921 5219620 818,593912 5219620 818))
(19 rows)

bounds=# select id, st_astext(geomtext) from small_tris;
 id |
st_astext
+---
  0 | POLYGON Z ((593890 5219590 840,593900 5219590 827,593890 5219600
817,593890 5219590 840))
  1 | POLYGON Z ((593890 5219600 817,593900 5219590 827,593900 5219600
815,593890 5219600 817))
  2 | POLYGON Z ((593900 5219600 815,593910 5219590 824,593910 5219600
815,593900 5219600 815))
  3 | POLYGON Z ((593910 5219590 824,593900 5219600 815,593900 5219590
827,593910 5219590 824))
  4 | POLYGON Z ((593910 5219600 815,593910 5219590 824,593920 5219590
842,593910 5219600 815))
  5 | POLYGON Z ((593900 5219600 815,593910 5219600 815,593900 5219610
815,593900 5219600 815))
  6 | POLYGON Z ((593890 5219600 817,593900 5219600 815,593900 5219610
815,593890 5219600 817))
  7 | POLYGON Z ((593890 5219620 812,593890 5219610 825,593900 5219610
815,593890 5219620 812))
  8 | POLYGON Z ((593890 5219630 827,593890 5219620 812,593900 5219620
841,593890 5219630 827))
  9 | POLYGON Z ((593900 5219610 815,593900 5219620 841,5938

Re: [postgis-users] Difficult Problem with Polygons

[Ed Linde]

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  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 > > wrote:
>>
>> Could you draw a figure ?
>>
>> Nicolas
>>
>> On 29 October 2012 11:03, Ed Linde > > 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 > > wrote:
>>  >>
>>  >> On 29 October 2012 21:33, Ed Linde > > 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  = 567 AND
>>
>>  >> ST_Relate(elements.geom, e.geom, 'FF2F11212');
>>  >>
>>  >> I'm not certain about your second question.
>>  >>
>>  >> -Mike
>>  >> __**_
>>  >> postgis-users mailing list
>>  >> 
>> postgis-users@postgis.**refractions.net
>> 
>> 

Re: [postgis-users] Difficult Problem with Polygons

[Stephen Woodbridge]

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 mailto:nicolas.ri...@gmail.com>> wrote:

Could you draw a figure ?

Nicolas

On 29 October 2012 11:03, Ed Linde mailto:edoli...@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 mailto:mwto...@gmail.com>> wrote:
 >>
 >> On 29 October 2012 21:33, Ed Linde mailto:edoli...@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  = 567 AND
 >> ST_Relate(elements.geom, e.geom, 'FF2F11212');
 >>
 >> I'm not certain about your second question.
 >>
 >> -Mike
 >> ___
 >> postgis-users mailing list
 >> postgis-users@postgis.refractions.net

 >> http://postgis.refractions.net/mailman/listinfo/postgis-users
 >
 >
 >
 > ___
 > postgis-users mailing list
 > postgis-users@postgis.refractions.net

 > http://postgis.refractions.net/mailman/listinfo/postgis-users
 >
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Re: [postgis-users] Difficult Problem with Polygons

[Nicolas Ribot]

Yes indeed it's clearer.

You could compute the distance between each adjacent triangle and the
voronoi generator and order by shortest distance. (taking the
triangle's centroid for the distance)
Also, is the voronoi boundary forming a polygon or just a line ? in
the former, you could find all the triangles inside the voronoi cell.
In the latter, you will have to determine a signed area or a cross
product to know if points lie in the same side of the boundary.

Nicolas

On 29 October 2012 13:45, Ed Linde  wrote:
> Hi All,
> Wondering if that diagram made things any simpler or is it still not clear
> what the problem
> is?
>
> Thanks,
> Ed
>
>
> On Mon, Oct 29, 2012 at 11:57 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 
>> wrote:
>>>
>>> Could you draw a figure ?
>>>
>>> Nicolas
>>>
>>> On 29 October 2012 11:03, Ed Linde  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  wrote:
>>> >>
>>> >> On 29 October 2012 21:33, Ed Linde  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 = 567 AND
>>> >> ST_Relate(elements.geom, e.geom, 'FF2F11212');
>>> >>
>>> >> I'm not certain about your second question.
>>> >>
>>> >> -Mike
>>> >> ___
>>> >> postgis-users mailing list
>>> >> postgis-users@postgis.refractions.net
>>> >> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>> >
>>> >
>>> >
>>> > ___
>>> > postgis-users mailing list
>>> > postgis-users@postgis.refractions.net
>>> > http://postgis.refractions.net/mailman/listinfo/postgis-users
>>> >
>>> ___
>>> postgis-users mailing list
>>> postgis-users@postgis.refractions.net
>>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>
>>
>
>
> ___
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>
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Re: [postgis-users] Difficult Problem with Polygons

[Ed Linde]

Hi All,
Wondering if that diagram made things any simpler or is it still not clear
what the problem
is?

Thanks,
Ed

On Mon, Oct 29, 2012 at 11:57 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 
> wrote:
>
>> Could you draw a figure ?
>>
>> Nicolas
>>
>> On 29 October 2012 11:03, Ed Linde  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  wrote:
>> >>
>> >> On 29 October 2012 21:33, Ed Linde  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 = 567 AND
>> >> ST_Relate(elements.geom, e.geom, 'FF2F11212');
>> >>
>> >> I'm not certain about your second question.
>> >>
>> >> -Mike
>> >> ___
>> >> postgis-users mailing list
>> >> postgis-users@postgis.refractions.net
>> >> http://postgis.refractions.net/mailman/listinfo/postgis-users
>> >
>> >
>> >
>> > ___
>> > postgis-users mailing list
>> > postgis-users@postgis.refractions.net
>> > http://postgis.refractions.net/mailman/listinfo/postgis-users
>> >
>> ___
>> postgis-users mailing list
>> postgis-users@postgis.refractions.net
>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>
>
>
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Re: [postgis-users] Difficult Problem with Polygons

[Nicolas Ribot]

Could you draw a figure ?

Nicolas

On 29 October 2012 11:03, Ed Linde  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  wrote:
>>
>> On 29 October 2012 21:33, Ed Linde  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 = 567 AND
>> ST_Relate(elements.geom, e.geom, 'FF2F11212');
>>
>> I'm not certain about your second question.
>>
>> -Mike
>> ___
>> postgis-users mailing list
>> postgis-users@postgis.refractions.net
>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>
>
>
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Re: [postgis-users] Difficult Problem with Polygons

[Ed Linde]

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  wrote:

> On 29 October 2012 21:33, Ed Linde  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 = 567 AND
> ST_Relate(elements.geom, e.geom, 'FF2F11212');
>
> I'm not certain about your second question.
>
> -Mike
> ___
> postgis-users mailing list
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>
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Re: [postgis-users] Difficult Problem with Polygons

[Mike Toews]

On 29 October 2012 21:33, Ed Linde  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 = 567 AND
ST_Relate(elements.geom, e.geom, 'FF2F11212');

I'm not certain about your second question.

-Mike
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Re: [postgis-users] Difficult Problem with Polygons

[Francois Hugues]

Hi,

1. Does st_touches not work for that ?

2. What do you mean by below ? south from the line ? St_distance should help 
you to find the closer one from Q.

Hugues.


 Message d'origine
De: postgis-users-boun...@postgis.refractions.net de la part de Ed Linde
Date: lun. 29/10/2012 09:33
À: PostGIS Users Discussion
Objet : [postgis-users] Difficult Problem with Polygons
 
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.

2. Then I have a line that cuts through a triangle's face and a point Q,
away from this line and
triangle. I would like to know amongst the neighbours of the triangle
(calculated in 1),
which ones fall *below* the line and closer to the point Q (where Q is the
generator of a Voronoi cell).
And also the set of triangles that are *above* the line and further from Q.

Any suggestions as to how I can go about achieving this in postgis 2.0?

Cheers,
Ed

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[postgis-users] Difficult Problem with Polygons

[Ed Linde]

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.

2. Then I have a line that cuts through a triangle's face and a point Q,
away from this line and
triangle. I would like to know amongst the neighbours of the triangle
(calculated in 1),
which ones fall *below* the line and closer to the point Q (where Q is the
generator of a Voronoi cell).
And also the set of triangles that are *above* the line and further from Q.

Any suggestions as to how I can go about achieving this in postgis 2.0?

Cheers,
Ed
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