Re: Box query

From: J M Davitt <jdavitt_at_aeneas.net>
Date: Sat, 22 Apr 2006 02:31:09 GMT
Message-ID: <Nzg2g.4791$YI5.515@tornado.ohiordc.rr.com>

Bob Badour wrote:
> Mikito Harakiri wrote:
>

>> Mikito Harakiri wrote:
>>
>>> Given a set of n-dimensional boxes
>>>
>>> table boxes (
>>>    dimension# integer,
>>>    low   integer,
>>>    high  integer
>>> )
>>>
>>> find all the pairs that intersect...
>>
>>
>>
>> And those pairs supposed to be what? Right, box ids:
>>
>> table boxes (
>>      *id*   integer,
>>      dimension# integer,
>>      low   integer,
>>      high  integer
>> )
>>

>
> select b1.id as box1, b2.id as box2
> from boxes b1, boxes b2
> where b1.id < b2.id
> and not exists (
> select 1 from boxes b3, boxes b4
> where b3.id = b1.id
> and b4.id = b2.id
> and b4.dimension# = b3.dimension#
> and (b4.high < b3.low or b4.low > b3.high)
> )
> group by 1, 2
> ;

Excellent! "not exists (no overlaps)." I like it. I was thinking "exists (all overlap)."

I think

       and (b4.high <= b3.low or b4.low >= b3.high)

prevents responses where the boxes abut each other; although not stated, I don't think that sharing part of an edge - even a single point - means that boxes intersect. I'm guessing the volume of the intersection s/b > 0. Received on Fri Apr 21 2006 - 21:31:09 CDT