[gdal-dev] highly compressed vector format for points

[Ragi Burhum]

Hello Peter,

The approach of scaling values into integers, if I recall correctly, is also
used in the transfer protocol for ArcSDE. I have considered this as an
option and was wondering if any of the non-ESRI datasources used that
approach.

I have seen the second method you describe being used for avoiding "small
feature shakiness" (yes, I made that word up) in 3D globes when zoomed-in
too close.

Thank you Peter for the response - I will definitely keep these options in
the bag of tricks if I end up having to implement a new datasource.

Thanks,

- Ragi



On Tue, Jul 6, 2010 at 11:18 PM, Peter J Halls <P.Halls at york.ac.uk> wrote:

> 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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