[postgis-users] Intersection of LineStrings

[Stephen Woodbridge]

Gist is an r-tree like index, only use if on the geometry column.

-Steve

On 6/6/2012 11:10 AM, Ed Linde wrote:
> Hi Steve,
> What indexes can I put on the linestring column? Is there an option of
> using a R-Tree index?
>
> Thanks,
> Ed
>
> On Wed, Jun 6, 2012 at 4:54 PM, Stephen Woodbridge
> <woodbri at swoodbridge.com <mailto:woodbri at swoodbridge.com>> wrote:
>
>     On 6/6/2012 9:57 AM, Ed Linde wrote:
>
>         Hi All,
>         Simple question. I have a table with half a million linestring
>         geometries, and I want to compute the
>         intersection points and also the linestring pairs that intersect
>         with
>         each other.
>         How can I do this? Is there an index that can avoid having to do a
>         self-join and computing
>         the intersections?
>
>
>     Create a spatial index on your table of linestrings and do a self join
>
>     select a.gid, b.gid, st_intersection(a.the_geom, b.the_geom)
>       from linestrings a, linestrings b
>       where a.the_geom && b.the_geom and st_intersects(a.the_geom,
>     b.the_geom);
>
>     You might get away with using this instead for the where:
>
>       where st_dwithin(a.the_geom, b.the_geom, 0.0);
>
>     Which might be faster.
>
>     The result will potentially be a collection if there is more then
>     one intersection and/or might be a linestring if the intersection is
>     an overlap along some part of the two strings.
>
>     -Steve
>
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