RE: [Geopriv] RE: [Ecrit] Location information in emergency sessioninitiation, need for time and accuracy?

Hi Carl,

Thanks for the input.
I guess as far as I see it, this should go one of two ways.
Either, stipulate RFC-3825 as representing a point only, in which case a
specification is required to make this clear and unambiguous.

Or

A specification is required expressing how to interpret the encoding
scheme such that the problems around the equator, prime meridian and
other arbitrary locations are not encountered.

I don't mind which, but a problem exist and supporters of the RFC-3825
mechanism should seek to resolve it. Until such time as it is resolved
this specification should only be used with a great deal of caution.

Cheers
James

> -----Original Message-----
> From: creed@opengeospatial.org [mailto:creed@opengeospatial.org]
> Sent: Monday, 11 September 2006 6:36 PM
> To: Winterbottom, James
> Cc: John Schnizlein; geopriv@ietf.org; Marc Linsner; ecrit@ietf.org
> Subject: Re: [Geopriv] RE: [Ecrit] Location information in emergency
> sessioninitiation, need for time and accuracy?
>
> This conversation peaked my interest. I have just looked at RFC-3825.
Not
> having been privy to all the original discussions and decisions, I am
a
> fresh set of "eyes" looking at this document. I think what we have
here is
> a failure to communicate due to ambiguous semantics in 3825. I may be
> wrong in this perception, but . . .
>
> My interpretation is that what is being defined is a uncertainty shape
in
> which the location of the device falls. As such, it is not truly a
point.
> A point in Euclidean geometry has no size, orientation, or any other
> feature except position. This is the basis of the ISO/OGC definition
for a
> point geometry.
>
> Take the following example. We draw a point by placing a dot with a
> pencil. This dot may have a diameter of 0.2mm, but a point has no
size. No
> matter how far you zoomed in, it would still have no width.
>
> What this discussion is really about is the fact that a point
geometry,
> whose location is defined by a lat/long coordinate, also has
properties.
> These properties include estimates of accuracy and precision. Very
simply
> stated: If the actual value is 4.321 and you say that it is 4.30, then
you
> are precise to the first decimal place but inaccurate by .021. There
are
> also properties of error and uncertainty. All these four properties
are
> very well defined in the literature. For example see:
> http://scidiv.bcc.ctc.edu/Physics/Measure&sigfigs/B-Acc-Prec-Unc.html
>
> So, what I would suggest is that perhaps 3825 be modified to very
clearly
> disambiguate the semantics of the terms being used. I suspect that
what
> "resolution" is really referring to is a description of the
uncertainty of
> the measurement. The point being measured falls somewhere in the area
of
> certainty. The shape of this area (yes, it is an area/polygon)
actually
> has a pretty strange shape if one transforms from lat/long to some
other
> coordinate reference system, such as State Plane.
>
> Regards
>
> Carl
>
>
> > So you are saying that the examples in the appendix of RFC-3825 are
> > wrong, and that RFC-3825 cannot and never will describe an area?
> >
> > It didn't die in Geopriv, I was waiting for you to actual come back
with
> > an explanation, what you did was write back an email that was
totally
> > irrelevant to the discussion. So I am still waiting!
> >
> >
> >
> >
> >
> >> -----Original Message-----
> >> From: John Schnizlein [mailto:jschnizl@cisco.com]
> >> Sent: Sunday, 10 September 2006 10:49 AM
> >> To: Winterbottom, James
> >> Cc: geopriv@ietf.org; Marc Linsner; ecrit@ietf.org
> >> Subject: Re: [Ecrit] Location information in emergency
> > sessioninitiation,
> >> need for time and accuracy?
> >>
> >> What part of "geographic location of the client" is unclear to you?
> >>
> >> It is beyond comprehension how this could be interpreted as a area
> >> rather than a point, with the resolution of the measurement of that
> >> point explicitly included in the location information.
> >>
> >> Why is this old argument being rehashed in the ecrit WG when if
> > finally
> >> seemed to die (mercifully) in GeoPriv?
> >>
> >> On Sep 9, 2006, at 6:11 PM, Winterbottom, James wrote:
> >>
> >> > So I am going to ask you. Point, or area?
> >
> >
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> >
> >
>
>

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Received on Mon, 11 Sep 2006 04:02:09 -0500