expressing uncertainty in degrees has been answered. With the
beautiful amount of detail in recent answers; I may have missed it.
Kind regards
Stephen
2009/7/29 Ivan Shmakov <oneingray@gmail.com>:
>>>>>> Richard Barnes <rbarnes@bbn.com> writes:
>
> >> Q) shall the draft specify such uncertainty, or shall it leave that
> >> to an external specification?
>
> > The draft should specify an uncertainty radius in meters, either as a
> > basic element or as a parameter.
>
> And once again, I wonder, how uncertainty in meters is supposed
> to be mapped to uncertainty in degrees?
>
> Please consider the following examples.
>
> * Assignment #1: drawing uncertainty on a world map
>
> Given the world map drawn in (longitude, latitude) coordinate
> system with WGS 84 as the datum (you may use the world.dat file
> shipped with Gnuplot for a crude ``continents only'' world map),
> draw the shape corresponding to a spherical circle of the given
> radius, with the given point as its center.
>
> You will get more credits if you use a Mercator-projection map
> instead.
>
> * point: 83.75N 53.36E, radius: 500000 m.
>
> * Use case #1: omit insignificant digits
>
> How do you transform a geo: URI specifying both location (using
> `wgs84' as the coordinate system) and uncertainty (in meters) so
> that the insignificant digits will be omitted?
>
> * geo:53.36,83.75;crs=wgs84;uncertaintyradius=50000
>
> * Use case #2: spatial relationship
>
> The application is given a number of geo: URIs specifying both
> location (`wgs84') and uncertainty (meters; varies.) Is there a
> simple way to find how the locations given are related? Do
> these URI specify completely distinct locations, or can some of
> them, taking the uncertainty into account, indeed code the same
> location?
>
> As an example, could you please point the URIs out of the
> following list that can be suspected of being related to the
> same object, just expressed with different precision?
>
> * geo:53.36,83.75;crs=wgs84;uncertaintyradius=30000
> geo:53.3,83.7;crs=wgs84;uncertaintyradius=10000
> geo:52.53,85.17;crs=wgs84;uncertaintyradius=20000
>
> * Use case #3: mapping geo: URIs to mapping services
>
> The current version of the draft reads:
>
> --cut: http://www.ietf.org/id/draft-ietf-geopriv-geo-uri-01.txt --
> <p>one of Vienna's popular sights is the <a href='geo:
> 48.198634,16.371648;crs=wgs84'>Karlskirche</a>.
>
> A web brower could extract the coordinates from the HTML snippet, and
> offer the user various options (based on configuration, context), for
> example:
>
> ...
>
> o switch to a mapping service of the user's choice once the link is
> selected
> --cut: http://www.ietf.org/id/draft-ietf-geopriv-geo-uri-01.txt --
>
> The URL to switch to Google Maps could be constructed as
> follows:
>
> http://maps.google.com/maps?ll=LATITUDE,LONGITUDE&spn=LAT-SPAN,LON-SPAN
>
> where LATITUDE and LONGITUDE are the coordinates, and LAT-SPAN,
> LON-SPAN give the extent of the map (``spans''; in degrees) to
> be displayed.
>
> The uncertainty specified within the geo: URI could be related
> to the scale (i. e., LAT-SPAN, LON-SPAN) of the map. How do you
> calculate the spans given some uncertainty expressed in meters?
>
> * Use case #4: travelling to Kemerovo
>
> Before travelling to Kemerovo you have taken a look at its
> Wikipedia page [1] and learned its geo: URI:
>
> geo:55.36083,86.08889;crs=wgs84;uncertaintyradius=5000
>
> [1] http://en.wikipedia.org/wiki/Kemerovo
>
> Travelling to Kemerovo by car, you've glanced at your GPS and
> read:
>
> geo:55.38400,86.09200;crs=wgs84;uncertaintyradius=42
>
> Do you expect to see the city around, or not yet?
>
> * Use case #1 re-visited: absolute uncertainty
>
> --cut: http://www.av8n.com/physics/uncertainty.htm --
> 1.2 How Should Uncertainty Be Expressed?
>
> If you want to express the uncertainty, express it separately and
> explicitly. For example, absolute uncertainty can be properly
> expressed as 1.234(55) or equivalently 1.234+-0.055. Relative
> uncertainty can be expressed as 2900+-13%.
> --cut: http://www.av8n.com/physics/uncertainty.htm --
>
> Given the following geo: URI, how could the absolute uncertainty
> of the coordinates be calculated?
>
> geo:53.36,83.75;crs=wgs84;uncertaintyradius=50000
>
> * And finally, ...
>
> ... given how trivial the cases above become when the
> uncertainty is expressed using the same units as used for the
> coordinates, why should the obstacles be invented?
>
> --
> FSF associate member #7257
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