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

[Obe, Regina]

Also noticed we have this same exercise repeated for touches, crosses, covers, within, disjoint.  I guess pretty much any function where we would normally do an && in PostgreSQL before it hits these functions.
 
The only place it doesn't seem redundant is in disjoint, but then again why don't we have disjoint using && in PostgreSQL.
 
wouldn't we just restate ST_Disjoint to use indexes by doing the below
 

 SELECT  NOT ($1 && $2)  OR _st_disjoint($1, $2) 
 
Thanks,
Regina
 
 
 
 
 

 
________________________________

From: postgis-devel-bounces at postgis.refractions.net on behalf of Obe, Regina
Sent: Mon 9/8/2008 3:14 PM
To: postgis-devel at postgis.refractions.net
Subject: [postgis-devel] What's the point of this exercise in intersects?


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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