[postgis-users] noding problem

[Paul Ramsey]

Yes, that's true. Hadn't thought of that one...

On 29-Oct-07, at 5:29 AM, Obe, Regina wrote:

> 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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