Subject: Re: draft-ietf-geopriv-dhcp-lci-option-oo.txt

From: [email-masked]
Date: Tue, 13 May 2003 10:40:01 -0400

Marc,

I suggest that a codepoint be added in Section 2 of "Internet
draft-ietf-geopriv-dhcp-lci-option-oo.txt" to represent the North American
Datum 1983 (NAD83) in addition to WGS84.

Fred Latham, a colleague who participates in the Open GIS Consortium,
provided the following background as rationale for this additional
codepoint.

NAD83 is an earth-centered (or geocentric) datum with reference point at
the center of the earth.
It is derived from Geodetic Reference System (GRS80), developed by USDOD
from satellite measurements.
(WGS84 is also derived from GRS80, although from a different reference
point.)
NAD83 has been adopted as the official datum by federal civilian agencies,
including the US Census Bureau, USGS, and US Geological Survey.
Internationally, several Canadian provinces and government agencies such as
the Canadian Department of Energy, Mines and Resources use NAD83. Mexico
has
also adopted NAD83 as its official datum.

WGS84 was developed by US  Defense Mapping Agency. This datum is a global
datum based on electronic technology which is still to some degree
classified.
WGS-84 is becoming the base datum for the processing and
conversion of data from one datum to any other datum.
The Global Positioning System (GPS) is based on this datum.

The difference between WGS-84 and NAD83 is small, and is generally
considered to be insignificant.
NAD83 and WGS84 are close enough to be called the same for non-geodetic
applications like Search and Rescue (the difference is about 2 meters).

Since a number of existing GIS databases used in Public Safety
implementations do use NAD83,
it seems reasonable to include this codepoint for the this application, one
of whose purposes is to support emergency calling.

Thanks,
Nadine Abbott

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From: "James M. Polk" <[email-masked]>
Date: Tue, 13 May 2003 10:23:39 -0500

>Datum 1983 (NAD83) in addition to WGS84.

This is the first time I've heard a request for NAD83. Is the USDOD going 
to continue using NAD83, or is it going to/in the process of converting to 
WGS84?

Do you know when the conversion is expected to be completed (if so)?

Do you why not (if they're not)?

just trying to get scope on this

>of whose purposes is to support emergency calling.

cheers,
James

            *************************************
        "The road to destruction is well traveled and crowded,
if you choose to get on that road, destruction will hit you head on"

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From: "James M. Polk" <[email-masked]>
Date: Tue, 13 May 2003 11:27:20 -0500

>just trying to get scope on this

Also (and not meaning to pile on here ;-) this document has only specified 
2 Measurement Units (MU)  for Altitude (meters and floors). Is there not an 
issue with that limitation as well?

Meters was chosen for measurements from the bottom of the ocean to the top 
of Everest; most aircraft could be covered in meters as well.

Satellites traveling at 18,000+ mph at altitudes of 100, 150, 250, 360 
miles above sea level makes precise positioning interesting with regard to 
speed, but there will need to be another MU for altitude (miles or 
kilometers) to represent these heights. Kilometers or miles do achieve 
geo-synchronous orbit altitude (~ 22,500 miles), but it is not yet 
specified because not enough people thought this would be relevant in IP 
for some time to come.

Another ID/RFC in the future could easily address orbital issues such as 
these (km or miles as a new MU being defined) when IP becomes appropriate 
for the situations.

I've been told that US satellites/constellations will not use IP for 
location for years to decades. I don't have first hand knowledge of the 
intentions from other countries at this time.

For Public Safety, I have no objections to adding NAD83 to this ID if 
others don't object.

cheers,
James