uncertainity of celestial objects' orbits' are expressed. e.g. +/-
0.7"
2009/7/28 Ivan Shmakov <oneingray@gmail.com>:
>>>>>> Thomson, Martin <Martin.Thomson@andrew.com> writes:
>
> [...]
>
> >>> 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
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