I'd actually like to see text that says that 'geo:1,2' == 'geo:1.0000,2.00000' to avoid this issue/trap entirely.
> -----Original Message-----
> From: geopriv-bounces@ietf.org [mailto:geopriv-bounces@ietf.org] On
> Behalf Of Ivan Shmakov
> Sent: Tuesday, 28 July 2009 10:27 AM
> To: geopriv@ietf.org
> Cc: Ivan Shmakov
> Subject: Re: [Geopriv] geo: URI: what about uncertainty?
>
> >>>>> Alexander Mayrhofer <alexander.mayrhofer@nic.at> writes:
>
> >> Any particular reason not to allow for an uncertainty information
> to
> >> be specified in the URI?
>
> > I am definitely not the expert who had addressed that for previous
> > protocols, but i remember there was always a heated discussion (3825
> > comes to my mind).
>
> ACK.
>
> > First, there's a difference between "uncertainty" and "object
> > dimension" (uncertainty is how "unsure" the measurement is, while
> > what you describe is more "what is the approx. Size of the location
> > to be represented).
>
> To my mind, these are not as distinct as it may seem.
>
> For example, I could post a geo: URI to describe my own position
> for, say, today. I'm certainly to go visit a few places during
> the day (at least home and work), so there's uncertainty
> associated with my position, and it comes not from the
> instrument's inability to perform the precise measurement, but
> also from my own ``inability'' to stay precisely in one place.
>
> In other words, the uncertainty always gives the interpreting
> party the area (for 2D) or volume (for 3D) where the object is
> most likely (at 95% confidence) to be found. The respective
> extents depend, and could be estimated from: the precision of
> the instrument, the characteristic size of the object which
> location is being measured, its characteristic movement
> distance, the intended use of the information being published,
> or, I believe, most commonly, taking into account all of these.
>
> The above being said, I don't think that a geo: URI may need to
> allow for a detailed specification of all the sources of the
> uncertainty, or why they were assumed, or how they were
> estimated or measured. However, the simply ``uncertainty as
> delta'' specification is, I guess, will be handy.
>
> One more example: in different contexts, either of the following
> may be used to refer to the city of Barnaul:
>
> * geo:53,83;
>
> * geo:53.4,83.8;
>
> * geo:53.36,83.75.
>
> While these aren't ``equal'' per the geo: scheme specification,
> the addition of the uncertainty information could allow for
> these to be related to each other.
>
> Also, it should be noted, that for a physicist, the following
> URIs look quite /distinct/:
>
> * geo:53.4,83.8;
>
> * geo:53.40,83.80.
>
> While these are ``equal'' per the specification. Don't know if
> it's of any significance, though. It may, however, be useful to
> note in the specification that the interpretation of the geo:
> URIs is somewhat contrary to the expectations a physicist may
> have.
>
> > Then, what is the "dimension" of those values? Is is a circle, or a
> > sphere? In "natural" space, or in the "projected" space (lat/lon
> > circle, which would definitely not give a circle in "real world"?)
> > What is the dimension (meters, inches, degrees?).
>
> In my opinion, it should always refer to the ``projected''
> space, and use the dimensions used for that projected space.
> For EPSG 4979, for instance, it would be degrees for Y and X,
> and meters for the altitude.
>
> > If you want, we can set up a quick chat here in Stockholm about it
>
> ? Could you please be more specific?
>
> It'd certainly be hard for me to visit Stockholm in the
> foreseeable future.
>
> > - and i would love to have someone who was involved in other
> > "uncertainty" discussions joining...
>
> --
> FSF associate member #7257
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