Hi Ben,
Can you do something with this as a sub-select:
select gid, st_area(st_intersection(a.the_geom, b.the_geom)) as size
from tablea a, tableb b
where a.the_geom && b.the_geom and size is not null
order by size desc limit 1
Hopefully, st_area() can deal with collections that might include points
and linestrings, or you will have to dump and filter the intersection
results.
I would be interested in see your query if you get something to work.
-Steve
On 6/6/2011 5:35 PM, Ben Madin wrote:
G'day all,
I've just realised that in selecting a group of properties by the
local government area they reside in, I end up with duplicates = some
properties span shire boundaries. I've used st_intersects, because
some properties cover boundaries, so I need those that are within and
may be partially without the boundary.
I'm sure I'm not the first person to have this problem, but I was
wondering if anyone has any insights into the most efficient way to
choose a unique listing of property and shire. I was wondering about
taking the area of the property still within the local government
area, and choosing the row with the biggest value...
Although I have unique property identifiers, I can't be sure of not
getting a ridiculous answer - an erroneously small amount of a
property in a shire etc.
My current query looks a bit like :
SELECT DISTINCT ON (pic) lga_name09 as shire, propname as name, pic
FROM lga l JOIN qldproperties q ON st_intersects(q.the_geom,
l.gda_geom) AND l.gid in (245,247,252,254,258,259,275,279,289,297);
but I need to do better than using SELECT DISTINCT ON.
cheers
Ben
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