Hello,
I'm trying do clip some geometry tables (very big) using a donut geometry.
This geometry is the difference between a site area and a buffer area
arround de same site.
I wrote:
SELECT r.*, ST_Intersection(r.the_geom, m.the_geom) AS int_geom FROM
big_table AS r,
(SELECT ST_Difference(b.the_geom,a.the_geom) as the_geom from (select
st_buffer(a.the_geom,buffer_radius) as the_geom from
(select the_geom from designprocess.dp_zn_boundaries AS r where r.type
= site_name) as a) as b,
(select the_geom from designprocess.dp_zn_boundaries AS r where r.type
= site_name) as a) AS m
WHERE ST_Intersects(r.the_geom, m.the_geom);
but it's to slow.
In what order should I do the operation? Intersection, difference, buffer...
Can any one help me.
Thanks,
júlio
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