RE: [Geopriv] Re: Geolocation Policy Draft Update

From: Thomson, Martin ^lt;Martin.Thomson@andrew.com>
Date: Wed Oct 03 2007 - 19:22:06 EDT

I was going to disagree with the change, because I always thought that the condition was the best part of the draft. I changed my mind. The condition isn’t ready. Lisa's points on usability uncovered deeper concerns about determinism.

One point I'd like to clear up was over the maintainability of the condition. I'd like to think that for users who are managing geospatial data, assumed access to a map is reasonable.

That aside, the polygon shape is somewhat restrictive and quite clumsy. Speaking from experience, user interface for polygons is a pain. A circle would be better. In the spirit of extensibility, allowing any shape but making one particular shape mandatory would be better. A circle is easier to manage and understand - 100m from this point. It also avoids some of the determinism concerns.

This leads straight to the heart issue. The draft makes a central assumption about the nature of location data. There is a clear assumption that the location of the Target is a point, with no uncertainty.

I'd argue that the assumption is bad. In the location business, you need to be comfortable with a degree of uncertainty. Virtually all results are some sort of probability distribution, usually with uncertainty that is significant enough to cause trouble. 50 metres 67% of the time is pretty vague by many standards - and that's actually pretty good in the overall spectrum of results for mobile networks. Ignoring uncertainty just leads to bad results.

That leads to two approaches, both equally valid, but both requiring additional work. In the first, you strive for determinism and you specify rigid rules for the handling of uncertainty. This means documenting algorithms and requiring strict adherence. Alternatively, you could start caring less about guaranteeing results and build tolerances in wherever the data is used.

From this perspective, the group needs to reconsider how such things are done. This also applies to loc-filters, where a similar function is defined.

On a related note - the assumption made in the draft means that the transformations described can seriously damage a location that includes uncertainty. A polygon that is transformed, point by point, can actually be totally invalid. Furthermore, a receiver can no longer assume that circle and similar results are accurate to any degree of confidence, since the uncertainty is not appropriately modified.

Cheers,
Martin

> -----Original Message-----
> From: Tschofenig, Hannes (NSN - DE/Munich)
> [mailto:hannes.tschofenig@nsn.com]
> Sent: Wednesday, 3 October 2007 1:30 AM
> To: ext Sam Hartman; Hannes Tschofenig
> Cc: GEOPRIV; Tim Polk; Russ Housley; Chris Newman; eric.gray@ericsson.com
> Subject: AW: [Geopriv] Re: Geolocation Policy Draft Update
>
> I am waiting for the group to provide us some feedback on the proposed
> change ...
>
> Ciao
> Hannes
>
> > -----Ursprüngliche Nachricht-----
> > Von: ext Sam Hartman [mailto:hartmans-ietf@mit.edu]
> > Gesendet: Dienstag, 2. Oktober 2007 17:23
> > An: Hannes Tschofenig
> > Cc: GEOPRIV; Tim Polk; Russ Housley; 'Chris Newman';
> > eric.gray@ericsson.com
> > Betreff: [Geopriv] Re: Geolocation Policy Draft Update
> >
> > Does the WG actually have consensus to remove location-specific
> > conditions?
> >
> >
> > _______________________________________________
> > Geopriv mailing list
> > Geopriv@ietf.org
> > https://www1.ietf.org/mailman/listinfo/geopriv
> >
>
>
> _______________________________________________
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Received on Wed, 3 Oct 2007 18:22:06 -0500

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