Re: [Geopriv] Proposal for uncertainty

No mechanism to collect location, especially civic location, is error free.

There is a statistical probability a civic location supplied as “THE” location of some target is incorrect.
It might be a small probability, it may be hard to calculate what it is, but there is some probability.

With enough data, it IS possible to quantify the error.  I think we will be able to do that in environments like emergency calling.

So, I’d like to see some language addressing the issue.

Brian

On May 23, 2014, at 8:48 PM, Roger Marshall <RMarshall@telecomsys.com<mailto:RMarshall@telecomsys.com>> wrote:

I would agree that getting everyone to agree on how they see probabilities used with civic addresses is a stretch.  Yet, the fact that the draft now allows for 100%, yet with cautionary language is a good thing to have.

All the other changes looks good to me.

Thanks Martin.

-roger marshall.

From: Henning G Schulzrinne [mailto:hgs@cs.columbia.edu]
Sent: Friday, May 23, 2014 4:28 PM
To: Martin Thomson
Cc: GEOPRIV WG; Marc Linsner; Roger Marshall; Ray Bellis
Subject: Re: [Geopriv] Proposal for uncertainty

This is a reasonably-well known problem and seems similar to the "there is a 30% chance that it rains today" - it either rains, or it doesn't. The same can be said about a "home detection" algorithm that is based (for example) on some inferences (e.g., time of day and last GPS coordinates). In that context, it does make sense to say "there's an 80% chance that the caller is at home", which really means "in 80% of cases with the same amount of information, the person was indeed at home". It's relatively easy to calculate the weather case (although there's the rumor that weather forecasts over-predict rain since nobody complains if their BBQ does NOT get rained out), but probably hard for our case, given the lack of retrospective ground truth.

Henning

On Fri, May 23, 2014 at 4:12 PM, Martin Thomson <martin.thomson@gmail.com<mailto:martin.thomson@gmail.com>> wrote:
I spoke about the one remaining issue with -uncertainty yesterday with
Ray.  That conversation, along with Roger's comments regarding
automated location determination helped me realize what I think the
source of the disconnect here is.

Based on this, I've tentatively concluded that the difference between
civic and geodetic location is not what is at the core of the issue,
though it's probably true that the issue only manifests with civic
location information.  Primarily because of our better intuition
regarding civic addresses.

The core of the concern is that confidence - as a statistical measure
- doesn't really make any sort of sense for location information that
is a bald assertion, as opposed to locations that are generated by
some measurement process (and here I give a nod to Carl for pointing
out reverse geocoding as an example of a measurement process that ends
with civic location).  For example, the assertion "I am at home" is
verifiable and basically either correct or not, usually the former.

It's only when taken in a larger context that terms like "confidence"
even apply.  In particular, that means automated location
determination.

I've taken a stab at clarifying this in the draft.

I've also permitted 100% confidence in the schema.  At the same time,
I've retained the text describing this as impossible, but that text is
all in the context of the statistical work, so I hope that the
introductory material makes that clear enough.

The changes are here:
https://github.com/martinthomson/drafts/commit/c2207408af95de74d1f4bb7d790965d69d4b3045
A readable copy is here:
http://martinthomson.github.io/drafts/draft-ietf-geopriv-uncertainty.html

Happy as always to take suggestions.  I'd like to think that this
helps address Marc's concern without needing to cut Section 3.3
entirely.

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