[gdal-dev] highly compressed vector format for points

[Peter J Halls]

Ragi,

    ESRI implemented something on these lines in the Personal Geodatabase, in an 
attempt to overcome data value restrictions in Access: they scaled the values 
into integers.  This approach would work for the application you describe, but 
loses precision further from the origin.  The scaling factor is stored separately.

    For some work I did, many years ago now, when working with a graphics 
package that could only handle 16bit coordinate values, I held the most 
significant part of the eastings and northings separately, subtracting it from 
the actual coordinates and adding it back on when I required the full value. 
This is simple and would work well for your application.

Best wishes,

Peter

Ragi Burhum wrote:
> Hello there,
> 
> The other day I got a question from someone that wanted to store a
> relatively small amount of point features (~31K) that are close to each
> other in a 'highly compressed' format. He wants to be able to query features
> by proximity using coords. The reason for this requirement is that he wants
> to be able to use it in embedded devices with limited memory. Yes I know
> memory is cheap and keeps getting cheaper, but I still thought it was an
> interesting question.
> 
> I can think of many ways to create a custom binary format to do such a
> thing, but I wanted to check the brain collective to hear what people
> thought. Of course spatialite and their new "compressed geometries" feature
> will come up in this conversation. I already sent an e-mail to that group
> for details about that :)
> 
> I want to be able to avoid reinventing the wheel, so what are your thoughts
> on this?
> 
> Thanks,
> 
> - Ragi
> 
> 
> 
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-- 
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Peter J Halls, GIS Advisor, University of York
Telephone: 01904 433806     Fax: 01904 433740
Snail mail: Computing Service, University of York, Heslington, York YO10 5DD
This message has the status of a private and personal communication
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