RE: altitude reference system

Hi Eric,

The definition is clear enough without resorting to discussions of gravitational models.  The term "ellipsoid" does not introduce any ambiguity; no mention is made of the geoid, which is clear enough.  EGM96 (or EGM2008) can be applied ad hoc by those who require "sea level" type altitude.

Obviously, this represents a (extremely minor) disconnect between the results and the actual physical environment; given the inherent limitations of the technology with respect to accuracy, I hardly think that it will have much bearing on the usability of the information.

Cheers,
Martin

> -----Original Message-----
> From: public-geolocation-request@w3.org [mailto:public-geolocation-
> request@w3.org] On Behalf Of Erik Wilde
> Sent: Tuesday, 23 December 2008 7:30 AM
> To: public-geolocation@w3.org
> Subject: altitude reference system
> 
> 
> hello.
> 
> congratulations for the first draft! a nice holiday gift!
> 
> since my altitude comments so far have not made it into the draft, i am
> splitting them, because they are two different issues. or are they
> captured in some open issue list? if so, please provide a pointer.
> 
> "The altitude attribute denotes the height of the position, specified
> in
> meters above the [WGS84] ellipsoid. If the implementation cannot
> provide
> altitude information, the value of this attribute must be null."
> 
> there has to be some indication of whether this value takes the EGM96
> data account or not. both are valid choices of a client using GPS
> measurement, and will result in different values. a consumer of that
> data could even choose to retroactively apply the EGM96 correction, but
> for that, it needs to know whether the altitude provided through the
> API
> does already include this correction or not. i never received any
> replies to me previous emails about this issue, but technically
> speaking, if there is no flag indicating whether the altitude uses
> EGM96
> or not, there is simply not enough information about the reference
> system for this value.
> 
> cheers,
> 
> dret.
> 

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Received on Sunday, 4 January 2009 23:43:19 UTC