[fdo-internals] FDO RFC 16 - FDO Provider for SQLite

[Kenneth, GEOGRAF A/S]

I can't figure out how to extract/compute the BBOX from an SQLite BLOB, 
without parsing the geometry.
I belive that it is faster to read the BBOX values rather than a 
potentially large BLOB field.

I agree that it would use some space to add the columns, but adding the 
columns would enable a fast filtering of unused features.
As for the 4 times index, one could merely add index for the x values, 
and then use sequential filtering for the y values.

Is your internal spatial index algorithm absolutely without benefit from 
added BBOX columns?

Regards, Kenneth, GEOGRAF A/S



Traian Stanev skrev:
>
>  
>
> It's a waste of space to store BBOX. It would cost at least 32 bytes 
> per feature, not counting the indexes.
>
>  
>
> Also, you can easily compute the bounding box and add those 4 columns 
> very quickly when you need them, given that SQLite is pretty fast to 
> read from. Indexing on the 4 BBOX columns would make spatial queries 
> have to compute the intersection of the results of 4 tree searches. 
> SQLite is fast, but it's not **that** fast.
>
>  
>
> Anyway, the nice thing about this format is that you can create the 
> BBOX columns anyway, and use them. The FDO provider will not be using 
> it though, for performance reasons.
>
>  
>
>  
>
> Traian
>
>  
>
>  
>
>  
>
> *From:* fdo-internals-bounces at lists.osgeo.org 
> [mailto:fdo-internals-bounces at lists.osgeo.org] *On Behalf Of *Kenneth, 
> GEOGRAF A/S
> *Sent:* Tuesday, March 25, 2008 7:12 AM
> *To:* FDO Internals Mail List
> *Subject:* Re: [fdo-internals] FDO RFC 16 - FDO Provider for SQLite
>
>  
>
> I just re-read the RFC.
>
> What are your reasons for not storing BBOX releated data in the data 
> table?
>
>
>
> I would suggest adding four columns, like minx, maxx, miny, max 
> (perhaps name them via. the geometry_columns table?).
> With that approach, and index on the pairs would move the BBOX query 
> load/optimization into the DBMS.
> BBOX queries are simple, and does not require reading the actual 
> column data.
>
> Your extended spatial index algorithm might read these values to 
> produce the search tree.
>
> Another suggestion, would be to store the search tree in a blob column.
> That would enable a much faster load of data.
>
> To avoid the requirement that all data updaters know the algorithm, it 
> might be legal to just clear the BLOB data on updates.
>
> I wrote a short paper on a similar mechanism some time ago, with a friend:
> http://www.hexad.dk/opensource/spatialdbms.pdf
>
>
>
> Regards, Kenneth, GEOGRAF A/S
>
>
>
> Traian Stanev skrev:
>
> Hello,
>
>  
>
> I just posted FDO RFC #16. Fresh off the virtual presses (printed on 
> 100% recycled electrons, for you green-minded folks):
>
>  
>
> http://trac.osgeo.org/fdo/wiki/FDORfc16
>
>  
>
>  
>
> Thanks,
>
> Traian
>
>  
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