RFC 1876 (rfc1876) - Page 3 of 18
A Means for Expressing Location Information in the Domain Name System
Alternative Format: Original Text Document
RFC 1876 Location Information in the DNS January 1996
than a "plus or minus" value. (This was chosen to match
the interpretation of SIZE; to get a "plus or minus" value,
divide by 2.)
VERT PRE The vertical precision of the data, in centimeters,
expressed using the sane representation as for SIZE. This
is the total potential vertical error, rather than a "plus
or minus" value. (This was chosen to match the
interpretation of SIZE; to get a "plus or minus" value,
divide by 2.) Note that if altitude above or below sea
level is used as an approximation for altitude relative to
the [WGS 84] ellipsoid, the precision value should be
adjusted.
LATITUDE The latitude of the center of the sphere described by the
SIZE field, expressed as a 32-bit integer, most significant
octet first (network standard byte order), in thousandths
of a second of arc. 2^31 represents the equator; numbers
above that are north latitude.
LONGITUDE The longitude of the center of the sphere described by the
SIZE field, expressed as a 32-bit integer, most significant
octet first (network standard byte order), in thousandths
of a second of arc, rounded away from the prime meridian.
2^31 represents the prime meridian; numbers above that are
east longitude.
ALTITUDE The altitude of the center of the sphere described by the
SIZE field, expressed as a 32-bit integer, most significant
octet first (network standard byte order), in centimeters,
from a base of 100,000m below the [WGS 84] reference
spheroid used by GPS (semimajor axis a=6378137.0,
reciprocal flattening rf=298.257223563). Altitude above
(or below) sea level may be used as an approximation of
altitude relative to the the [WGS 84] spheroid, though due
to the Earth's surface not being a perfect spheroid, there
will be differences. (For example, the geoid (which sea
level approximates) for the continental US ranges from 10
meters to 50 meters below the [WGS 84] spheroid.
Adjustments to ALTITUDE and/or VERT PRE will be necessary
in most cases. The Defense Mapping Agency publishes geoid
height values relative to the [WGS 84] ellipsoid.
Davis, et al Experimental