Dave Potts wrote:
I am trying to discover all the data points when a river system crosses
a road system, my data is expressed as two different shapefiles, I had
assumed that it was just a case of calling the Intersection method
eg. select m.name from transport m , rivers r where
Intersection(r.the_geom,m.the_geom) = 't';
But I get a 'parse error- invaid geometry when I try this, is this the
correct way of doing this?
Start by:
select count(*) from transport where not is_valid(the_geom);
select count(*) from transport where not is_valid(the_geom) and not
is_valid(buffer(the_geom, 0.0));
If the later clears up all the issues then do:
update transport set the_geom = buffer(the_geom, 0.0);
and do the same for rivers.
If you still have errors you will need to load those geometries into
other software to fix them. of you can ignore them by filtering them out
of the intersection query.
Also intersection returns the geometry of the intersection. if you just
want the boolean it is intersects() and you should add a gist index to
the_geom column on both tables and
select m.name from transport m , rivers r where
m.the_geom && r.the_geom and -- use index
is_valid(m.the_geom) and is_valid(r.the_geom) and -- add filter bad
intersects(r.the_geom,m.the_geom); -- boolean test
-Steve W
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