Subject: RE: [Ecrit] Geodetic interpretations

From: "James Winterbottom" <[email-masked]>
Date: Thu, 31 Mar 2005 12:09:11 +1000

I am not sure that I agree with you entirely here as I stated, for polygons
and arcbands (both of which are used today for cellular), they either do not
specify a centre point, or the point that is specified is not in the closed
shape (arcband), so what would you do in these cases? You probably need to
do some sort of polygon inclusion or intersection mapping anyway.

I also don't think that you are right about this not having an impact on
routing. If a point resides in one boundary, but 90% of the closed
uncertainty shape resides in a different boundary, a point only routing
solution will misroute the call. This is analogous to simply using
cell-sector for cellular routing which, according to some sources, results
in about 30% of calls being misrouted.

I am not saying that we would not route on point only, but we could specify
preferences and indicate why these have been chosen. I think that
restricting ourselves to a single point solution only does not lend itself
so well to network determined location techniques (particularly for
wireless) as the points represent boundaries or references rather than
client/device specific location.

-----Original Message-----
From: Henning Schulzrinne [mailto:[email-masked]] 
Sent: Thursday, 31 March 2005 11:48 AM
To: Winterbottom, James [WOLL:5500:EXCH]
Cc: [email-masked]
Subject: Re: [Ecrit] Geodetic interpretations

I'm not sure what you would do differently for routing if you knew the 
confidence interval (which this is, roughly). You'd presumably always 
route on the center of circle or other geometric shape. Clearly, the 
dispatcher might find this useful to guess whether to send one squad car 
or a search party.

I'll repeat my rant from earlier: elaborate confidence measures are, in 
my view, largely bogus for dispatch and routing. (They are useful to 
characterize the performance of a technology.) They are usually based on 
not much more than "measured across thousands of points across the 
country, 90% of measurements fell within 100 m of true location", which 
says very little about the GPS satellite shading or the number and 
relative location of cell towers (for TOA-style measurements), say, at 
the corner of Main and 5th in Podunk, NY. Thus, if you were to 
repeatedly measure location at that point, you might only be off by 10 
m, or maybe it's a bad spot and it's always off by 200 m.

This would be useful if you could bound the technology resolution in all 
cases, i.e., that it is extremely unlikely to be wrong by more than X 
meters.

Thus, worrying too much about accuracy is like providing 
pound-to-kilogram conversions on noodle packages to 7 digits.

James Winterbottom wrote:
> Hi All,
> 
> I am going to change the subject a bit here from what has been going
> around the list to date about "validated locations".
> 
> I want to ask some opinions about geodetic information, and how we
> should seek to interpret this. For IETF-62 I presented a paper in the 
> GeoPriv working group that was authored by me, Hannes Tschofenig and 
> Martin Thomson on, amongst other things, what might be a required 
> minimal set of GML to implement to support routing applications. 
>
(http://www.ietf.org/internet-drafts/draft-winterbottom-geopriv-pdif-lo-prof
ile-00.txt)
> 
> In the presentation I indicated that we were going to look at
> uncertainty in more detail in the next edition, and confidence. The 
> difference being that an uncertainty is usually defined as being with X 
> metres of a provided Latitude/Longitude, and a confidence factor is a 
> percentage chance that you will reside in that area. PIDF-LO does not 
> support the notion of a confidence factor today, but this is something 
> that we plan to look at in the next iteration of the above draft in the 
> form of suggestions.
> 
> The wireless standards, at least those used in North America, 
> generally
> provide both. And the FCC for regulations are really only interested in 
> 2 confidence factors, the 67% and the 90%. This tends to lead to the 
> location representations as being closed shapes, circles, polygons, 
> arcbands etc, rather than single points. While a circle with uncertainty 
> can be expressed a s point with radius, neither a polygon or an arcband 
> can.
> 
> So where is this leading?
> 1) Do we care about confidence in location for routing?
> 2) If so, what is our minimal confidence level?
> 3) Do we have preferences in how location is to specified (see draft
> above)?
> 
> While these points may be lower level requirements, they are things 
> that
> we must start considering if we want an implementable solution.
> 
> Cheers
> James
> 
> 
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From: "Marc Linsner" <[email-masked]>
Date: Thu, 31 Mar 2005 09:49:39 -0500

Question: If the technology that determines location can't figure out where
you're at, how can the protocol that carries the data and/or the using
application figure it out?

Location determination is a hard problem, but I don't believe it's an IETF
problem, and certainly not an ecrit problem.  I believe, but I may be
convinced otherwise, that ecrit will require a location point to use for
routing.  This would require the location determination mechanism to make
its best guess at determining that point.  And, if it's routed wrong, that
is what selective transfer is all about, which is what happens with the 30%
miss-routes today.

-Marc-

 

  _____  

From: [email-masked] [mailto:[email-masked]] On Behalf Of
James Winterbottom
Sent: Wednesday, March 30, 2005 9:09 PM
To: Henning Schulzrinne
Cc: [email-masked]
Subject: RE: [Ecrit] Geodetic interpretations