[Mapserver-dev] virtualising attribute data

[Frank Warmerdam]

>> Attila Csipa wrote:
>>
>>> I was thinking about the possibilities of virtualising attribute data 
>>> for my needs, meaning that for example a layer that has spatial data 
>>> in a shapefile has the attribute data in plain mysql (this is how it 
>>> works in my prototype test and happens to be the most requested 
>>> feature that I got). Note that this is _not_ the same as doing a join 
>>> and not like using virtualspatialogr. 

Attila,

Could you explain a bit more how what you want to do is not a join?  You
will need to have some sort of index attribute on the spatial features
that you use to lookup the corresponding attribute record won't you?  Isn't
this effectively applying a join?

Stephen Woodbridge wrote:
> I for one would like to see a virtualised attribute capability in 
> mapserver because:
> 
> 1) setting up ODBC drivers are a real pain on Linux

I can sympathize with this.

> 2) currently joins are not supported on rendering
> 3) I have 100 GB of Census Summary file data in MySQL and would like to 
> render thematic maps of Tiger data in shapefiles
> 4) The prospect of learning PostGIS/postgre and moving all the Census 
> data and all the Tiger data to PostGIS just seems like an overwhelming 
> and time consuming task given all the other things I would like to be 
> doing.
>
> OK, so I'm probably not in the main stream, but I think that this would 
> be a good feature that other would use if it is available.

The problem is that there are lots of potential formats that folks might
have their attribute data in.  How do we avoid writing all sorts of
custom code inside MapServer?  The OGR virtual joins tries to push this
issue down OGR.  OGR uses ODBC so it doesn't need a custom driver for
every format.

Best regards,
-- 
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