Subject: [VCARDDAV] Geographic properties (issue 155): straw-man wording

From: Andy Mabbett <[email-masked]>
Date: Sun, 27 Jul 2008 18:05:48 +0100

Regarding "Geographic properties" (issue 155), I propose the following
two sets of straw-man wording; one for ADR and one for GEO. Clearly the
suggestions are incomplete and will, I hope, act as the basis for debate
with the aim of making the text both complete and robust. I have not
included justifications, which I have posted previously:

   <http://www.ietf.org/mail-archive/web/vcarddav/current/msg00473.html>

I have marked up optional components and comments with square brackets
using a pipe to separate suggested alternatives thus: [Do we want to
include this sentence. ?] and [beer|wine]. Such decisions are intended
to be resolved during this debate, and not carried into the final
wording.

For background and prior discussion please see:

        <http://microformats.org/wiki/geo-extension-nonWGS84>

        <http://microformats.org/wiki/luna>

        <http://microformats.org/wiki/mars>

and

        <http://microformats.org/wiki/geo-extension-elevation>

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7.3.1. ADR

[Addition of "vessel"; "continent"  and "body"]

   Special notes:  The structured type value consists of a sequence of
      address components.  The component values MUST be specified in
      their corresponding position.  The structured type value
      corresponds, in sequence, to the post office box; the extended
      address (e.g. apartment or suite number); the vessel (e.g. a ship
      or space vehicle); the street address; the locality (e.g., city);
      the region (e.g., state or province); the postal code; the country
      name; the continent; the body (e.g. Earth, Moon or Mars). When
      a component value is missing, the associated component separator
      MUST still be specified.

      Where no BODY is specified, a default value of "Earth"
      [SHOULD|MUST] be assumed.

   Examples: In the first example the post office box and the extended
   address are absent, and there are no vessel, continent or body.

           ADR;TYPE=home:;;;123 Main Street;Any Town;CA;91921-1234;;

   The second example refers to a ship at sea:

           ADR;TYPE=home:;Cabin 4b;RMS Queen Elizabeth 2;;;;;;

   The next example refers to a base near the South Pole:

           ADR;TYPE=work:;;;;;Utsteinen;;;;Antarctica;

   The final example refers to a base on The Moon:

           ADR;TYPE=work:;;Moonbase Alpha;;Plato;;;Moon

Issues:

   *    Should "BODY" be free text, or taken from values listed in a
        registry, or based on an existing protocol used in planetary
        astronomy, such as the Gazetteer of Planetary Nomenclature:

          <http://planetarynames.wr.usgs.gov/> ?

   *    Should each ADR (optionally) include a set of coordinates?

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7.5.2. GEO

[Addition of "schema", rules for Martian and similar coordinates]

   Purpose:  To specify information related to the global positioning of
      the object the vCard represents.

   Value type:  A single structured value consisting of two float values
   and a text value separated by the SEMI-COLON character (ASCII decimal
   59).

   Special notes:

        This property specifies information related to the global
        position of the object associated with the vCard. The value
        specifies latitude and longitude, in that order (i.e., "LAT LON"
        ordering), followed by the schema in use.

        If SCHEMA is unspecified [add "or not recognised" ?], a default
        of WGS84 should be assumed. [or "...the default schema for the
        body in question should be assumed." ?]

        When a SCHEMA is unspecified, the associated component separator
        MUST still be specified.

        In terrestrial and some other systems, including WGS84, the
        longitude represents the location east and west of the prime
        meridian as a positive or negative real number; and the latitude
        represents the location north and south of the equator as a
        positive or negative real number, respectively. Values are
        between 0 and 180.

        In other systems, such as IAU2000 for Martian coordinates,
        longitude values run from 0 to 360 Eastwards or 0 to 360
        Westwards: the latter should be represented by negative values.

   Examples (the first two are on Earth, and are exactly equivalent; the
   third is on Mars):

           GEO:37.386013;-122.082932;

           GEO:37.386013;-122.082932;WGS84

           GEO:37.386013;222.082932;IAU2000

Notes:

   *    Geographical longitude on, for example, Mars is not 180 degrees
        west to 180 degrees east: 18N,226E is a legal Martian location.

        http://www.esa.int/SPECIALS/Mars_Express/SEM0VQV4QWD_0.html
        says:

                Note that the modern standard for measuring longitude on
                Mars is "planetocentric longitude", which is measured
                from 0°–360° East and measures angles from the
                center of Mars. The older "planetographic longitude" was
                measured from 0°–360° West and used coordinates
                mapped onto the surface.

Issues:

   *    Is "schema" the optimal phrase, or should it be "DATUM" or
        "REFERENCE-FRAME"?

   *    Should SCHEMA be free text, or taken from values held in a
        registry?

   *    Do we also want an "elevation" (aka "altitude", "depth") value?

   *    Do we want to insist on 6 decimal places, or do we want to allow
        less-specific values for large areas, such as cities, mandating
        that trailing zeros are thus significant; and that the same
        number of decimal places SHOULD be used for latitude and
        longitude? The later model is used in hCard microformats, which
        are then converted to vCards.

   *    Should each ADR (optionally) include a set of coordinates? What
        about each AGENT?

   *    If so, do we wish to say that user-agents [MAY|MUST] generate a
        warning if a user attempts to enter, say, WSG84 as a schema with
        a body other than "Earth"? [but this [SHOULD|MUST] be allowed ?]

   *    Do we wish to say that agents MAY convert other terrestrial
        coordinates to WGS84 (or whatever) for storage and
        synchronisation?

   *    Do we wish to say that agents MUST not pass non-terrestrial
        coordinates to terrestrial services such as mapping tools (and
        so on)?

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Thank you for your interest.

-- 
Andy Mabbett
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