[postgis-devel] RE: standard deviation based histogram extent reduction

[Mark Cave-Ayland]

Hi strk,

> -----Original Message-----
> From: 'strk' [mailto:strk at keybit.net] 
> Sent: 10 June 2004 20:01
> To: Mark Cave-Ayland
> Cc: postgis-devel at postgis.refractions.net
> Subject: Re: [postgis-devel] RE: standard deviation based 
> histogram extent reduction
> 
> 
> I've added irregular sized histogram grid (cell aspect is 
> always nearly square keeping total cells near to requested precision).
> 
> I'd like to have some test results before working on other 
> refinements. Just to make sure we are not introducing any bug.
> 
> Thanks for you attention.
> 
> --strk;

The irregular sized histogram code looks good to me.

The only improvement I was suggesting was that instead of considering
the cutoff rectangle as being the overall histogram extent, we should
recalculate the histogram extent ignoring everything outside of this
rectangle. This would have the result in most cases of bringing in the
histogram extent much "tighter" around the dataset and hence increase
the accuracy - other than changing the histogram extents, it won't
change any of the existing code or methodology.


Cheers,

Mark.

---

Mark Cave-Ayland
Webbased Ltd.
Tamar Science Park
Derriford
Plymouth
PL6 8BX
England

Tel: +44 (0)1752 764445
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