[postgis-users] Re: Help with finding multi-variate clusters

[Paul Ramsey]

Dylan,

Are you calculating clusters on the fly? Do you need to? How about  
having a clusters table, that is hooked to your base data table with  
a trigger? That will be just as up-to-date as your base data, and  
only have to do the calculations once per data update.

Paul

PS. A distance threshold "cluster" will return lots of unexpected and  
unwanted results, which is why more sophisticated tricks have been  
developed.


On 13-Jul-05, at 6:57 AM, Eli Dylan Lorimer wrote:

> Hi Stephen,
>
> Thanks for your reply. I might look into writing that function as  
> you suggested, but I feel slightly limited in that I'm making the  
> SQL requests in the form of a WFS request to GeoServer which in  
> turn is speaking to PostGIS and so I'm not sure if I can add my own  
> functions and then have my WFS requests trigger them. I'll have to  
> look into this and figure it out.
>
> I see what you are saying, it being an iterative algorithm and not  
> really suited for set operations as such. Hum, I still feel like  
> with the spatial operators there must be a way to get what I'm  
> looking for, even if I have to make multiple WFS requests or  
> something.
>
> Maybe someone else on this list might know of a way to do this?
>
> Anyway, cheers.
> ./dylan
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