> >data. If the device does not know of or support the datum, then it
> >has no basis upon which to interpret the data.
> >
> >If a device does not understand the datum it MUST discard the data.
> >
> >If datum=4 is specified for locations on the moon, interpreting this
> >as WGS84 would lead to errors.
>
> this conclusion does not support a migration from one version to
> another (where one of the primary fields in the original version
> (i.e., the datum field) is what's being modified.
This is precisely why I objected to the inclusion of the "ver" tag.
> I put this to the WG, if they want to have some ver0 clients and some
> ver1 clients guaranteeing that *every* ver0 client will have zero
> location and zero means to inform anything or anyone that they have
> no location.
That was the decision that the WG made. Both Richard and I sent detailed analyses that dealt with this problem from both perspectives.
> Given that there is no statement in RFC 3825 like
>
> "If a device does not understand the datum it MUST discard the
> data."
>
> It's a heck of a time to try and introduce that ideal now.
But it's necessary. If you don't understand the datum, then you can't use the data. What if I decide that longitude zero runs through Moscow? Other datums in common use result in subtle errors in some areas, very much less subtle in others.
> further, as a matter of pragmatic coding, a non-fully compliant ver0
> implementation might not have support for datums other than WGS84,
> therefore, might not choose to have such a rigid enforcement of
> Martin's rule (of "confused about the datum, delete all location
> data").
>
> The obvious result will be that fewer existing client implementations
> will possess location once the first ver1 server is installed, and
> that shouldn't be the goal of anyone - given the main (but by no
> means only) driver/motivation is emergency calling.
>
> The practical result will be fewer emergency calls get to the correct
> PSAP.
Yes. Absolutely.
I don't like re-opening issues, because that shatters the illusion of progress. However, it seems that you weren't across the full ramifications of the decision, so maybe we need to re-open that one.
> James
>
>
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