Andrew, thank you, this is good information. To be sure we all
understand each other, please see comments below. Remember, this
mechanism we are proposing will be most useful for wired network
connections, the easiest type of device to locate (and currently the
largest type of connection used within an enterprise). Wireless devices
will have to employ a more exotic mechanism possibly at layer 1 or 2 for
a more precise device location.
> It depends on the jurisdiction. For instance, it is different in
Canada
> and the US - one uses mean lower low water and the other uses lowest
> normal tide or something as a nautical chart datum.
For those who are struggling with this, it is not our intention to
(re)define zero altitude. We are simply attempting to provide a
mechanism for people who understand altitude values to share them
amongst each other via a standardized mechanism. If one were to receive
such data, it is assumed that they will understand the definition of
zero altitude within the jurisdiction/authority from which the data
originated. Some map datum define zero altitude, some don't. For those
that don't, we define mean low tide.
>
> Defining elevation seems to be more problematic than defining
position.
> If consumer-grade GPS has a horizontal resolution between 5-30 metres,
> that's good enough to give a street or maybe a room in a building. But
the
> vertical resolution may be double that, and that's 3 floors at best,
even
> assuming you have ground level sorted out properly. Other navigation
> techniques such as LORAN (obsolescent) or cellphone-signal based may
not
> give elevation at all.
Hence our measurement unit of floors. We are expecting the altitude
data within the MU floors to be derived from the numbers on the wall
next to the elevators, not from a gps or similar device.
-Marc Linsner-
Received on Wed Jul 2 11:16:00 2003
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