[postgis-users] noding problem

[Obe, Regina]

P,

So does that mean you can create a more efficent st_dwithin that instead
of doing this

SELECT $1 && ST_Expand($2,$3) AND $2 && ST_Expand($1,$3) AND
ST_Distance($1, $2) < $3

Does this

SELECT $1 && ST_Expand($2,$3) AND $2 && ST_Expand($1,$3) AND
_ST_DWithin($1, $2, $3)


And the new _ST_Dwithin function would do exactly what distance does
except it would return a boolean and kick out a true as soon as it finds
a point set where the distance is < $3; no need to wait to reach 0.  

R

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paul
Ramsey
Sent: Thursday, October 25, 2007 10:50 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] noding problem

Yes, that is all the magic there is to the "distance is faster"  
assertion. Obviously it's only faster for cases where there are lots  
of fully contained candidates that return immediately on the first  
point test.

P

On 25-Oct-07, at 4:24 AM, Obe, Regina wrote:

>  Am I safe in saying that distance treats the case of distance() ==  
> 0 as
> a special case - e.g. you can't get lower than 0 for distance so there
> is no point in checking any further?

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