Subject: [Geopriv] Draft about DHCP Location using Point with Uncertainty Circle

From: Hannes Tschofenig <[email-masked]>
Date: Thu, 14 Feb 2008 21:36:21 +0200

Hi all,

I believe that there is a value (from a deployment point of view) in 
having a document that describes a way in DHCP to convey a point with an 
uncertainty circle.
This should be a pretty short and easy document. The conversion into GML 
is also easy!

Would someone be interested to write such a document with me? Don't want 
todo it alone.

Ciao
Hannes

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From: "James M. Polk" <[email-masked]>
Date: Thu, 14 Feb 2008 14:29:18 -0600

I believe that whole idea is against earlier stated WG agreements, 
since it is identical to an accuracy (with uncertainty) 
description.  This was decided in the early days of Geopriv that this 
would not be how we describe location (i.e., as a circle).  This 
should be found in the meeting minutes from 2002-2003 when we were 
writing RFC 3693 (Geopriv Requirements).

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From: Hannes Tschofenig <[email-masked]>
Date: Thu, 14 Feb 2008 22:42:35 +0200

Hmmm. You do not like my idea.

 From a deployment point of view that seems, however, quite useful since 
this is what WLAN equipment returns when I trust the people I asked; 
they have running code and played around with this stuff for years.

James M. Polk wrote:
> since it is identical to an accuracy (with uncertainty) description.  
> This was decided in the early days of Geopriv that this would not be 
> how we describe location (i.e., as a circle).  This should be found in 
> the meeting minutes from 2002-2003 when we were writing RFC 3693 
> (Geopriv Requirements).
>

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From: John Schnizlein <[email-masked]>
Date: Thu, 14 Feb 2008 16:14:54 -0500

You might want to ask your WLAN experts again.  The 95% confidence  
interval of (x,y) location being a circle would depend on an  
omnidirectional antenna and a single access point (and no obstacles  
or reflectors).  WLAN controllers can consider the radio power  
received by a station from two omnidirectional access points, which  
would narrow the 95% confidence interval to an elliptical region  
where the circles overlap.  The probability density cloud can be  
quite unlike a circle when walls or electrical equipment is also in  
the field.

But consider how little difference is implied between a location  
represented as two dimensions with resolution on each (rectangular  
near the equator) and an ellipse.  Especially if the errors are  
uncorrelated, the probability density in the corners outside the  
ellipse but with the rectangle is likely small.

What is the compelling reason to add the complexity of representing  
another shape for what is essentially unknown error distributions in  
practice?  It seems to me that all this proposal could do is give  
potential implementers fear (more work), uncertainty and doubt.

John

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From: "Winterbottom, James" <[email-masked]>
Date: Thu, 14 Feb 2008 19:03:04 -0600

> ellipse but with the rectangle is likely small.

John - you seem to be saying that the *intention* of 3825, which
provides two dimensional point with solution, is to convey a
quasi-rectangular area of uncertainty.  Is this correct?

Cheers
James

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From: Andrew Newton <[email-masked]>
Date: Fri, 15 Feb 2008 08:38:02 -0500

> This should be a pretty short and easy document. The conversion into  

This sounds like a good idea.  However, there is an OGC specification  
on binary XML that could allow you to describe a more generic  
mechanism.  Just a thought.

-andy

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From: Cullen Jennings <[email-masked]>
Date: Sat, 23 Feb 2008 21:08:52 -0800

> mechanism.  Just a thought.

Could you post a pointer to this. Sounds like a good thing to read.  
Thanks, Cullen