2.3. Latitude and Longitude Fields
The Latitude and Longitude values in this specification are encoded
as 34 bit, twos complement, fixed point values with 9 integer bits
and 25 fractional bits. The exact meaning of these values is
determined by the datum; the description in this section applies to
the datums defined in this document. This document uses the same
definition for all datums it specifies.
When encoding, Latitude and Longitude values are rounded to the
nearest 34-bit binary representation. This imprecision is considered
acceptable for the purposes to which this form is intended to be
applied and is ignored when decoding.
Positive latitudes are north of the equator and negative latitudes
are south of the equator. Positive longitudes are east of the Prime
Meridian (Greenwich) and negative (2s complement) longitudes are west
of the Prime Meridian.
Within the coordinate reference systems defined in this document
(Datum values 1-3), longitude values outside the range of -180 to 180
decimal degrees or latitude values outside the range of -90 to 90
degrees MUST be considered invalid. Server implementations SHOULD
prevent the entry of invalid values within the selected coordinate
reference system. Location consumers MUST ignore invalid location
coordinates and SHOULD log invalid location errors.
On Sun, Jan 23, 2011 at 2:49 AM, Andy Mabbett <andy@pigsonthewing.org.uk> wrote:
On 23 January 2011 00:27, Bernard Aboba <bernard.aboba@gmail.com> wrote:[...]
> Here is a proposed revision of Section 2.3 to address the concern. Comments
> welcome.
>
> 2.3. Latitude and Longitude Fields
geoURI (rfc5870) allows for a 'crs' (coordinate reference system)
> Longitude values encoded by the DHCP server MUST be normalized to the
> range from -180 to +180 degrees. Positive longitudes are east of the
> Prime Meridian (Greenwich) and negative (2s complement) longitudes
> are west of the Prime Meridian.
parameter so that, in future, coordinates on bodies such as The Moon
or Mars can be expressed. Some such CRSs allow a longitude value range
of 0-360, with no negative values, and of course these do not make
reference to Greenwich.
WGS84 is assumed as default, where no CRS is specified.
It would be sensible to build in such future proofing - and
consistency & compatibility - here, using the relevant sections of
GeoURI (3.4.1, 3.4.2) as a model.
See:
<http://tools.ietf.org/html/rfc5870#section-3.4.1>
<http://tools.ietf.org/html/rfc5870#section-3.4.2>
also <http://en.wikipedia.org/wiki/Geo_URI>.
--
Andy Mabbett
@pigsonthewing
http://pigsonthewing.org.uk
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