[Ietf-calsify] GEO in draft-ietf-calsify-rfc2445bis-07.txt

Mr. Demeanour mrdemeanour at jackpot.uk.net
Tue Jul 10 10:46:03 PDT 2007


Eliot Lear wrote:
> Steve,
> 
> Thanks for your comment.  Can you restate your point in a succinct 
> proposed textual change?

If I read it correctly, it doesn't call for a textual change. It's
simply pointing out that six decimal places/one meter may be spurious
precision (one could add prose to that effect, of course).
> 
> Eliot
> 
> Steve Allen wrote:
>> In the context of metrology I wonder about the text in 3.8.1.6.
>> Geographic Position
>> 
>> It says The longitude and latitude values MAY be specified up to
>> six decimal places, which will allow for accuracy to within one
>> meter of geographical position.
>> 
>> This is only true if the geodetic datum is specified.
>> 
>> I point out the US DoD's instructional page to soldiers on this 
>> http://earth-info.nima.mil/GandG/publications/horizdatum.html
>> 
>> At a more technical level I point out the partial list of datums in
>>  use at 
>> http://earth-info.nima.mil/GandG/publications/tm8358.1/tr83581b.html#ZZ23
>>  where in the links to the graphics for table 2 it is immediately 
>> evident that some older geodetic datums upon which available maps
>> are based differ by hundreds of meters from the more recent, 
>> satellite-geodesy-based datums.
>> 
>> In much the same vein as quoting the standards documents for UTC,
>> if the values used in this field are to be believed at a level of 1
>>  meter, then it is at the least necessary to require that the
>> latitude and longitude values be expressed in a standard geodetic
>> datum created no earlier than the year 1980.
>> 
>> -- Steve Allen                 <sla at ucolick.org>
>> WGS-84 (GPS) UCO/Lick Observatory        Natural Sciences II, Room
>> 165    Lat +36.99855 University of California    Voice: +1 831 459
>> 3046           Lng -122.06015 Santa Cruz, CA 95064
>> http://www.ucolick.org/~sla/     Hgt +250 m 


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