[postgis-users] St_intersection

[Jose Carlos Martinez Llario]

Hi,
According to SQL/MM and in PostGIS the intersection of two linestrings 
can be:

a Empty ST_Point (GeometryCollection  Empty in PostGIS 1.5)
a ST_Point
a ST_LineString
a ST_MultiPoint
a ST_MultiLineString
a ST_GeomCollection with ST_Point and ST_LineString.

Cheers,
Jose



On 19/03/2012 20:25, pcreso at pcreso.com wrote:
> Whenever the intersection of two lines is a linestring.
>
> eg:
> select astext(ST_intersection(ST_makeline(ST_Makepoint(0,0), 
> ST_Makepoint(1,1)),ST_Makeline(ST_Makepoint(0.5, 0.5), 
> ST_Makepoint(1.5,1.5))));
>          astext
> -------------------------
>  LINESTRING(0.5 0.5,1 1)
> (1 row)
>
> Brent
>
> --- On *Tue, 3/20/12, Bob Pawley /<rjpawley at shaw.ca>/* wrote:
>
>
>     From: Bob Pawley <rjpawley at shaw.ca>
>     Subject: [postgis-users] St_intersection
>     To: postgis-users at postgis.refractions.net
>     Date: Tuesday, March 20, 2012, 6:44 AM
>
>     Hi
>     I am querying a geometry looking for intersection point between a
>     line and an other geometry.
>     The return is 2 points and 2 linestrings. (when I use st_union a
>     geometry collection results)
>     Can anyone tell me under what conditions that a st_intersection
>     would return a linestring??
>     insert into num_search (the_geom3)
>     select st_intersection(Num_Search.the_geom1, entities.wkb_geometry)
>     from entities, Num_Search
>     where Num_Search.seq = 'R'
>     and st_intersects(entities.wkb_geometry, Num_Search.the_geom1) = True
>     Bob
>
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