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.ha...@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 >> >> >> >> ------------------------------------------------------------------------ >> >> >> _______________________________________________ >> gdal-dev mailing list >> gdal-dev@lists.osgeo.org >> http://lists.osgeo.org/mailman/listinfo/gdal-dev >> > > -- > > -------------------------------------------------------------------------------- > 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 > > -------------------------------------------------------------------------------- >
_______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev