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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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
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