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

Steve Allen sla at ucolick.org
Tue Jul 10 10:31:46 PDT 2007


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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