[postgis] distance(geometry,geometry) now in the CVS version

Dave Blasby dblasby at refractions.net
Tue Jul 24 13:47:37 PDT 2001

The distance() function is now in the CVS version.  

I've also put in expand(BOX3D,double d) which returns a new bbox which
is exanded d unit in all directions.

select expand('BOX3D(0 0 0, 100 100 100)', 100.0);
 BOX3D(-100 -100 -100,200 200 200)
(1 row)

also, because there's an auto-convesion between geometry and box3d, you

select expand('POINT(0 0 0)'::GEOMETRY, 100.0);
 BOX3D(-100 -100 -100,100 100 100)

This will allow you to do an index search using distances more easily.  
Lets say you take "A" as your base feature you're searching for nearby

select * from <table> where  distance(A,<geom_col>) <100 and  
<geom_col> && expand(A, 100) ;

<geom_col> && expand(A, 100):
	this does an index scan on the table looking for features that might be
100 units or less away from A.  It'll quickly filter out far away

distance(A,<geom_col>) <100 
	this returns true if the min distance from A to the geometry is less
than 100 units


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