Your observation raises the requirement that the document needs an
informative section on when to use 4326 and when to use 4979. For example,
it is quite valid to use EPSG 4326 and have an (x,y,z) coordinate. It is
also valid to use EPSG 4979 and have an unknown (z). Guidance for
implementers would be very useful. I can provide some words if everyone
thinks this is appropriate.
Carl
> I am assuming that if altitude is no known then the datum now becomes
> EPSG:4326 and not EPSG:4979?
>
> Cheers
> James
>
>> -----Original Message-----
>> From: geopriv-bounces@ietf.org [mailto:geopriv-bounces@ietf.org] On
> Behalf
>> Of Thomson, Martin
>> Sent: Tuesday, 9 June 2009 2:55 PM
>> To: geopriv@ietf.org
>> Subject: Re: [Geopriv] [geopriv] #8: Altitude type of 0 == no altitude
>>
>> I'll offer my opinion.
>>
>> Offering a way of stating that altitude is not known is useful. The
>> document should register altitude type of 0 and register the meaning
> to
>> indicate that the altitude is not known (note: this does not mean that
>> altitude = 0, any more than it indicates an altitude of 35,000km).
>>
>> Information on the implications of choosing to include no altitude
> should
>> be included in the description of each datum (including its impact on
> the
>> EPSG code and URN). GML conversion examples should note the impact of
>> this attribute.
>>
>> This opinion is extracted from draft-thomson-geopriv-3825bis. Text
> from
>> that document can be used to address this issue if this opinion is
>> supported by the consensus of the working group.
>>
>> --Martin
>>
>> > -----Original Message-----
>> > From: geopriv issue tracker [mailto:trac@tools.ietf.org]
>> > Sent: Tuesday, 9 June 2009 2:26 PM
>> > To: Thomson, Martin
>> > Cc: geopriv@ietf.org
>> > Subject: [geopriv] #8: Altitude type of 0 == no altitude
>> >
>> > #8: Altitude type of 0 == no altitude
>> >
> ---------------------------------------+-------------------------------
>> > -----
>> > Reporter: martin.thomson@andrew.com | Owner:
>> > Type: defect | Status: new
>> > Priority: major | Milestone:
>> > Component: rfc3825bis | Version:
>> > Severity: - | Keywords: altitude
>> >
> ---------------------------------------+-------------------------------
>> > -----
>> > RFC 3825 seems to indicate that an altitude type of 0 indicates
> that
>> > there
>> > is no altitude defined. This needs to be clearer in the bis.
>> >
>> > Q: is altitude type 0 valid?
>> >
>> > Q: what meaning is attached to altitude type 0?
>> >
>> > Q: what is the impact of having no altitude on the existing datum
>> > definitions?
>> >
>> > --
>> > Ticket URL: <http://trac.tools.ietf.org/wg/geopriv/trac/ticket/8>
>> > geopriv <http://tools.ietf.org/geopriv/>
>> >
>>
>>
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