[postgis-users] several SRID on one table

[Ben Madin]

Arguably the relational database concept is meant to avoid storing the  
same data more than once, but I have also done this to reduce overhead  
during complex output queries (ie storing a point on surface of a  
polygon instead of calculating it each time). Ultimately, it worked  
out slightly faster to have multiple smaller tables, as we only wanted  
one aspect of the geometry at any one time. When it came for time for  
others to use the same data, it was also much clearer to them what was  
going on.

It might be a good time to add that storing the same data in multiple  
formats requires some method to ensure concurrency - if someone  
updates the column that is in WGS84, a trigger to update the other  
columns would be essential to avoid returning mixed version  
information. This obviously holds true whether you have multiple  
columns in one table or multiple tables with one column each.

cheers

Ben



On 02/09/2009, at 3:13 , pcreso at pcreso.com wrote:

> H Steve,
>
> I have had recommendations that this is not good practice, but I  
> have done this often myself for various reasons, with good success.
>
> As far as I'm concerned, a very useful ability of a spatially  
> enabled RDBMS is to realise that a geometry is only an attribute of  
> an entity, like a date, time, numeric or string type. Real world  
> entities can be represented by multiple geometries, and have  
> multiple dates, etc,  associated with them, so this is a perfectly  
> good model, and offers substantial benefits over the (dated) GIS  
> model where the geometry is somehow more special than other  
> attributes of a feature/entity.
>
> Cheers,
>
>  Brent Wood
>
>
> --- On Wed, 9/2/09, Steve.Toutant at inspq.qc.ca <Steve.Toutant at inspq.qc.ca 
> > wrote:
>
>> From: Steve.Toutant at inspq.qc.ca <Steve.Toutant at inspq.qc.ca>
>> Subject: [postgis-users] several SRID on one table
>> To: "PostGIS Users Discussion" <postgis- 
>> users at postgis.refractions.net>
>> Date: Wednesday, September 2, 2009, 2:46 AM
>>
>>
>> Hello,
>>
>> We need to use a table for
>> several purposes
>> with different SRID.
>>
>> Is it a good practice to
>> have several
>> geometry columns on one table or should we create one table
>> per SRID?
>>
>> What are the pros and cons
>> of using
>> several geometry columns on one table?
>>
>>
>>
>> thanks
>>
>> Steve
>>
>>
>>
>> Steve Toutant, M.
>> Sc.
>>
>> Analyste en géomatique
>>
>> Secteur environnement
>>
>> Direction des risques biologiques, environnementaux et
>> occupationnels
>>
>> Institut national de santé publique du Québec
>>
>> 945, avenue Wolfe
>>
>> Québec, Qc G1V 5B3
>> Tél.: (418) 650-5115 #5281
>>
>> Fax.: (418) 654-3144
>>
>> steve.toutant at inspq.qc.ca
>>
>> http://www.inspq.qc.ca
>>
>>
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>>
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-- 

Ben Madin
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							Out here, it pays to know...


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