[postgis-devel] What's the point of this exercise in intersects?

[Paul Ramsey]

It gets better, since the bbox check often recurs in the GEOS code
base too. However, it's not exactly a high cost check, and there are
cases where there functions will be called sans indexes. Doing the
check in postgis potentially saves a trip to GEOS. The GEOS checks
have to be there to support pure-GEOS apps.

C'est la vie.

P.

On Mon, Sep 8, 2008 at 12:14 PM, Obe, Regina <robe.dnd at cityofboston.gov> wrote:
> I was looking at the lwgeom_geos_c.c intersects function - starting at line
> 2039 and was thinking isnt' this
> a bit redundant.  By the time we get into this function we have already done
> a bounding box check.  It probably isn't adding much overhead, but thought I
> would flag it as potentially redundant.
>
>  /*
>   * short-circuit 1: if geom2 bounding box does not overlap
>   * geom1 bounding box we can prematurely return FALSE.
>   * Do the test IFF BOUNDING BOX AVAILABLE.
>   */
>  if ( getbox2d_p(SERIALIZED_FORM(geom1), &box1) &&
>   getbox2d_p(SERIALIZED_FORM(geom2), &box2) )
>  {
>   if ( box2.xmax < box1.xmin ) PG_RETURN_BOOL(FALSE);
>   if ( box2.xmin > box1.xmax ) PG_RETURN_BOOL(FALSE);
>   if ( box2.ymax < box1.ymin ) PG_RETURN_BOOL(FALSE);
>   if ( box2.ymin > box2.ymax ) PG_RETURN_BOOL(FALSE);
>  }
>
>
> thanks,
> Regina
>
>
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