Hi,

I do some test.

I notice that the ST_OrderingEquals

return true only when two lines are perfectly identical (same sequence vertex too).

For example:

Select ST_OrderingEquals(
    ST_GeomFromText('LINESTRING(2 3, 3 2, 6 1)',3003 ),ST_GeomFromText('LINESTRING(2 3, 3 2, 6 1)',3003 )
)

But if I add a single vertex to one of lines it return false.
Select ST_OrderingEquals(
    ST_GeomFromText('LINESTRING(2 3, 3 2, 6 1, 8 9)',3003 ),ST_GeomFromText('LINESTRING(2 3, 3 2, 6 1)',3003 )
)

So it is not useful to detect the versus of lines because
the linestring of the line table is not sure they are perfectly identical to the definition of the boundary of polygons.
The boundary of polygons are always closed lines.
Instead the same closed arc may be require more lines of the line table.

More again:
even supposing the lines-table elements was closed like the boundary of polygons the ST_OderingEqual require they are
first vertex identical.

So this case of two lines identical, and same versus but different starting vertex, return false.

Select ST_OrderingEquals(
    ST_GeomFromText('LINESTRING(2 3, 3 2, 6 1, 8 9, 2 3)',3003 ),ST_GeomFromText('LINESTRING(3 2, 6 1, 8 9, 2 3, 3 2)',3003 )
)

Regards,


--
-----------------
Andrea Peri
. . . . . . . . .
qwerty àèìòù
-----------------

Hi

Hi all,

I think I've got a bit of a problem with snapping points to lines.  I had thought that using line_interpolate_point(..., line_locate_point(...)) would do the trick, but this seems not to be the case:

gis=# SELECT ST_AsText(v.the_geom), ST_SRID(v.the_geom), ST_AsText(r.the_geom), ST_SRID(r.the_geom) FROM road_segments AS r, venues AS v WHERE v.venue_id = 29 AND r.gid = 100982;

                st_astext                 | st_srid |                                    st_astext                                    | st_srid
------------------------------------------+---------+---------------------------------------------------------------------------------+---------
 POINT(415185.606066865 7827721.52951473) |   28353 | LINESTRING(415250.679102704 7827994.85292521,415218.694181662 7827642.44920486) |   28353
(1 row)

gis=# SELECT ST_Intersects(ST_line_interpolate_point(r.the_geom, ST_line_locate_point(r.the_geom, v.the_geom)), r.the_geom) FROM road_segments AS r, venues AS v WHERE v.venue_id = 29 AND r.gid = 100982;

 st_intersects
---------------
 f
(1 row)

gis=# SELECT postgis_full_version();

                                  postgis_full_version                                 
----------------------------------------------------------------------------------------
 POSTGIS="1.4.1" GEOS="3.2.1-CAPI-1.6.1" PROJ="Rel. 4.7.1, 23 September 2009" USE_STATS
(1 row)



Any assistance would be much appreciated.

Thanks,

-Francis Markham

Hi Mehmet,

When you imported the shapefile, the SRID you are meant to specify is the SRID of the data, not the SRID you want.  Since the data is in Dubai Local TM, the SRID is 3997.  To get the transformation you want, try the following:

select   ST_AsText( ST_Transform(centroid(ST_SetSRID(the_geom, 3997)),4326)) from ult.test2 limit 5;