Re: [dhcwg] Fwd: Working Group Last Call: Location Configuration

Cecil

Thank you for your comments, and I would be interested in your offer to
review the document.

 From what subsections you provided, sections 5.26 and 6.60 seem flawed (or
I don't understand the integer numbering reference -7 to +7). As our
discussion here has made painfully clear, this LRMS also doesn't answer the
question of "what is vertical (or altitude) = 0?" other than when
referencing the ground level of a building.

For example, I'm in Vienna, Austria right now - what is ground level? There
are a few fairly large water bodies within this city that appear to be a
substantially below ground level relative to the ground level right next to
it (all rivers here seem to have concrete vertical walls *up* to the street
or dirt ground level). Some would argue that mean low sea level doesn't
mean anything to a country that is land-locked (like Austria is).

By contrast, in San Francisco, ground level varies quite a bit from
building to building that happen to be right next to each other in sections
of that city, yet there is an ocean mean (or mean high, or mean low) sea
level to relate to the ground level close by.

Were these two sections (5.26 and 6.60) intentionally left this vague, or
is there still some work here to be done?

Please don't take my comments as an attack, just an observed hole or
inconsistency that I'm open to have filled in/resolved.

At 11:28 AM 7/10/2003 -0400, cwgoodwin@earthlink.net wrote:
>To all:
>
>As someone who has been working on location referencing for Intelligent
>Transportation Systems for years for the USDOT ITS standards program, I
>have been following with interest the recent discussion in this group on
>datums. FYI, what follows is a set of extracts from a new SAE standard
>about to go to ballot (ATIS committee), called the Location Referencing
>Message Specification (LRMS). The LRMS specifies data concepts and
>messages for a variety of coordinate based and non-coordinate based
>location referencing methods. Note in the extracts that much of what you
>have been discussing is in the standard. With respect to units, altitude
>is in 'Distance' units, which are a choice of integer or real expressions
>for different English and Metric units. A complete XML Schema is part of
>the standard, and I would be glad to provide the complete draft to members
>of this group who would be interested in being official reviewers of the
>standard.
>
>Also related to the discussion on WGS-84 and ITRF, an ISO TC204
>sub-working group is developing an international location referencing
>standard for ITS location referencing between navigation databases. While
>this standard is not complete, ITRF has been accepted as the standard
>geodetic datum, being more acceptable to our non-US members than WGS-84.
>
>Dr. Cecil W. H. Goodwin
>1564 Blue Heron Ln
>Jacksonville Beach, FL 32250
>Phone/Fax: 904-246-2264
>Email: cwgoodwin@earthlink.net
>
>--------------- excerpts --------------
>
>5.15 Data Frame: GeoLocation:frame
>
>Use: The GeoLocation sub-profile conveys a two- or three-dimensional
>geographic location. The standard horizontal datum for a spot location is
>WGS-84; other horizontal datums can be specified by
>HorizontalDatum. Vertical Datum is an option within height.
>
>ASN.1 Representation:
>
>GeoLocation ::= SEQUENCE {
> latitude Latitude,
> longitude Longitude,
> horizontalDatum HorizontalDatum OPTIONAL,
> height Height OPTIONAL
> }
>
>------------------------------------
>
>
>5.26 Data Frame: Height:frame
>
>Use: A vertical height expressed as either an altitude with respect to a
>vertical datum, or a vertical level from -7 to +7, where level 0 is the
>ground surface, or ground level of a structure.
>
>ASN.1 Representation:
>
>Height ::= CHOICE {
> altdatum SEQUENCE {
> altitude Distance,
> verticalDatum VerticalDatum OPTIONAL
> },
> verticalLevel VerticalLevel
> }
>
>--------------------------------------
>
>6.17 Data Element: HorizontalDatum:cd
>Use: The underlying horizontal geodetic datum for a geographic coordinate.
>
>ASN.1 Representation:
>
>HorizontalDatum ::= ENUMERATED {
> wgs-84 (0),
> wgs-84egm-96 (1),
> nad83 (2),
> nad27 (3)
> }
>
>------------------------
>
>6.59 Data Element: VerticalDatum:cd
>
>Use: The underlying vertical geodetic datum for a geographic coordinate.
>
>ASN.1 Representation:
>
>VerticalDatum ::= ENUMERATED {
> wgs-84 (0),
> navd (1),
> ...}
>
>---------------------------
>
>6.60 Data Element: VerticalLevel:qty
>
>Use: Vertical level specified as an ordinal class expressed positive
>(above) or negative (below) the ground surface or ground level of a
>structure. (vertical level code = 0).
>
>ASN.1 Representation:
>
>VerticalLevel ::= INTEGER (-7..7)
>
>XML Representation:
><xs:simpleType name="VerticalLevel" >
> <xs:restriction base="xs:byte">
> <xs:minInclusive value="-7"/>
> <xs:maxInclusive value="7"/>
> </xs:restriction>
></xs:simpleType>
>
>----------------------
>

cheers,
James

                                *******************
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Received on Mon Jul 14 11:12:53 2003