There has been considerable discussion on uncertainty in this group. You
may wish to read relevant emails and documents.
That said, in geodesy a simple approach (and one that is often used),
positional and local uncertainty become simple indicators of the quality
of position. Positional uncertainty is global or absolute, computed with
respect to the reference frame or datum. Local uncertainty is computed
with respect to adjacent features within the same data set or source.
There are many excellent references on uncertainty and geodetic
coordinates. Just google "geodesy uncertainty".
The point is that this group - in coordination with others such as the OGC
- has invested considerable time discussing uncertainty and how to express
such information within the context of the requirements as defined by this
community. As such, how uncertainty is viewed and expressed is different
than in the traditional GIS industry (where uncertainty is often ignored!)
which is mapping uncertainty and not uncertainty related to an observation
and measurement (as in sensors).
Happy to discuss more if you like :-)
Carl
> [...]
>
> >>> SI units are good.
>
> >> ... Except that these would be quite hard to apply to the (latitude,
> >> longitude) pairs as specified by the geo: URIs.
>
> >> The location specification reading ``53 degrees latitude plus/minus
> >> 1000 meters, ...'' seems rather unsound to me. I'd expect the
> >> deltas' dimensions to align with the corresponding axes' dimensions,
> >> as per the CRS used.
>
> [...]
>
> > You make a good point. Maybe it would be best to leave the
> > complexity out and we can discuss this in a separate draft.
>
> No objections here, but I'm completely unfamiliar with the
> ``draft process.''
>
> > This would specify a new "uncertainty" URI parameter and its
> > semantics.
>
> I'd rather opt for a set of per-axis parameters.
>
> > I support the idea of uncertainty and would be willing to help.
>
> > On the point of metres uncertainty, that's how we do it.
>
> How ``we'' is defined here?
>
> > For one thing, that makes it more usable by people.
>
> I don't think so. One point is whether we're going to have a
> single, or several (one per axis), uncertainty values.
>
> If the latter way is choosen, how would one apply an uncertainty
> specified in meters to a value in degrees (like a longitude)?
>
> The former way is no better, as one, once again, cannot easily
> reconstruct the area (or volume) within which the object is to
> be most likely positioned. At least, one'll have to transform
> the projected space's (x', y', z') triplet to the Euclidean
> space, make a sphere in that space, using the uncertainty as the
> radius, and then transform this sphere back to the projected
> space. I didn't much research into these ``volume
> tranformations'', but it seems overly complex to me.
>
> ... Especially when compared to simply making an axes-aligned
> ellipsoid in the selected projected space.
>
> To put it simple, one's going to take a long way to simply draw
> the object's likely position area with MapServer (or GRASS),
> while with the per-axis, axis-aligned parameters it's simple and
> straightforward.
>
> --
> FSF associate member #7257
> _______________________________________________
> Geopriv mailing list
> Geopriv@ietf.org
> https://www.ietf.org/mailman/listinfo/geopriv
>
_______________________________________________
Geopriv mailing list
Geopriv@ietf.org
https://www.ietf.org/mailman/listinfo/geopriv
