Re: AW: [Geopriv] Re: Geolocation Policy Draft Update

From: Carl Reed OGC Account ^lt;creed@opengeospatial.org>
Date: Thu Oct 04 2007 - 16:49:43 EDT

There is a huge amount of literature in the Geography/photogrammetry
community about uncertainty and confidence in mapped data. One of the world
experts on this topic lives a mile or so from me here in Colorado. I would
look to that community if we are seeking a general solution and not one
specific to cellular.

Regards

Carl

----- Original Message -----
From: "Dawson, Martin" <Martin.Dawson@andrew.com>
To: "GEOPRIV" <geopriv@ietf.org>
Cc: "Tim Polk" <tim.polk@nist.gov>; "Russ Housley" <housley@vigilsec.com>;
"ext Sam Hartman" <hartmans-ietf@mit.edu>; "Chris Newman"
<chris.newman@sun.com>; <eric.gray@ericsson.com>
Sent: Thursday, October 04, 2007 1:41 PM
Subject: RE: AW: [Geopriv] Re: Geolocation Policy Draft Update

> Any polygon is a representation of uncertainty iff the intent is to
> communicate that the location of the *subject* of the application is
> somewhere within that polygon. Of course a civic address is conveying
> the same uncertainty information with respect to the point if the intent
> is that the location is somewhere within that civic address. The only
> difference is that one quantifies the geographic extent of the
> uncertainty explicitly and the other only implicitly.
>
> Actually, I think it's only true that a PIDF-LO doesn't communicate
> uncertainty if you're using it in an application that says that the
> communicated shape exactly represents the actual subject of the
> communication. I think the more common use case is the one described
> above.
>
> It's silly to say that the communication of uncertainty is a cellular
> thing. If I provide a polygon that represents the boundary of my
> property with the intent of saying that the actual subject of the
> exchange is somewhere (and anywhere) within that property, then I have
> just communicated an uncertainty. The polygon clearly didn't have to be
> determined in the context of cellular communications.
>
> I think there may be - not sure - some confusion with confidence; which
> would actually apply a percentage value to the probability that the
> subject is within the boundary of the provided polygon and not outside
> it. Indeed, PIDF-LO does not provide a mechanism to communicate
> confidence. But, also, I don't think that confidence need only apply to
> cellular. For example, you might provide a more constrained polygon in a
> property boundary scenario because 95% of the time the subject occupies
> a 10% subset of the larger polygon. Again, this is nothing to do with
> whether it's a cellular context or not.
>
> Cheers,
> Martin
>
> -----Original Message-----
> From: James M. Polk [mailto:jmpolk@cisco.com]
> Sent: Friday, 5 October 2007 5:10 AM
> To: Tschofenig, Hannes (NSN - DE/Munich); Thomson, Martin; ext Sam
> Hartman; Hannes Tschofenig
> Cc: GEOPRIV; Tim Polk; Russ Housley; Chris Newman;
> eric.gray@ericsson.com
> Subject: Re: AW: [Geopriv] Re: Geolocation Policy Draft Update
>
> At 09:32 AM 10/4/2007, Tschofenig, Hannes (NSN - DE/Munich) wrote:
>> >
>> > 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.
>>
>>Please note that PIDF-LO does not have an explicit way to express
>>uncertainty.
>
> This is on purpose, because there are many ways of expressing
> location without a means to determine uncertainty (at the end of a
> wire, for example, or connected to a specific AP at a known location
> as another). Forcing "uncertainty" where it doesn't belong (PIDF-LO
> is *not_only* for cellular networks) does more harm than good -
> because it starts to make techs guess what is the right percentage of
> uncertainty. Further, the idea that uncertainty applies only to
> coordinate representations is wrong. For example, I can give you a
> linear ring of the 5 points of my house's property, with my
> property's boundary being straight lines between each point (which is
> true BTW) - and claim that is the same as my civic
> address. Therefore, if there is uncertainty in my polygon of my
> house, there is uncertainty in my civic street address I can give out
> as well - yet time and time again this has been said to be untrue.
>
> James
>
>
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Received on Thu, 4 Oct 2007 14:49:43 -0600

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