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Re: BUG #5745: geometry bug?

From: Mike Fowler <mike(at)mlfowler(dot)com>
To: Jin <jindiax(at)gmail(dot)com>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #5745: geometry bug?
Date: 2010-11-10 16:08:48
Message-ID: 4CDAC390.9030903@mlfowler.com (view raw or flat)
Thread:
Lists: pgsql-bugs
On 10/11/10 10:08, Jin wrote:
> The following bug has been logged online:
>
> Bug reference:      5745
> Logged by:          Jin
> Email address:      jindiax(at)gmail(dot)com
> PostgreSQL version: 8.4.5
> Operating system:   windows xp pro sp3
> Description:        geometry bug?
> Details:
>
> The distance of the horizontal lseg and the point on that is inaccurate.
>
> select point(1.0,1.0)<->  lseg'(0.0,0.0),(2.0,0.0)';
> ↓
> result 1.4142135623731
>
> must be 1.0
>
> P.S.
> I'm sorry about if it was already reported.
> Because I can't read English well.
>    

 From my digging it appears that this is returning the distance between 
the first point in the line and the individual point. To get 1.0 you 
would be looking for the the distance between the midpoint of the line 
and the individual point which can be achieved with:

SELECT POINT(1.0,1.0) <-> POINT(LSEG'(0.0,0.0),(2.0,0.0)');

Digging through the documentation I can't find anything that says which 
point should be used in the line for distance comparisons. So I would 
rephrase this bug as:

The distance of the horizontal lseg and the point is calculated against 
the first point in the line. Should this be calculated against the 
midpoint of the line instead?

Regards,

-- 
Mike Fowler
Registered Linux user: 379787


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Subject: Re: BUG #5745: geometry bug?
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