This attribute specifies the geodetic
(or equivalently, geocentric) longitude of the observer, in degrees, measured positive eastwards. See
also attribute
ObsLat. The basic
Frame class makes no use of this attribute, but specialised subclasses
of Frame may use it. For instance, the
SpecFrame,
SkyFrame and
TimeFrame classes use it. The default
value is zero.
The value is stored internally in radians, but is converted to and from a degrees string for
access. Some example input formats are: " 155:19:23.2" , " 155 19 23.2" , " 155:19.387" , "
155.32311" , " E155.32311" , " -204.67689" , " W204.67689" . As indicated, the sign of the
longitude can optionally be indicated using characters " E" and " W" in place of the usual "
" and "
-" . When converting the stored value to a string, the format " [s]ddd:mm:ss.ss" is used, when " [s]" is
" E" or " W" and the numerical value is chosen to be less than 180 degrees.
Frame
All Frames have this attribute.
SpecFrame
Together with the ObsLon,
Epoch,
RefRA and
RefDec attributes, it defines the Doppler shift introduced by the observers diurnal
motion around the earths axis, which is needed when converting to or from the topocentric
standard of rest. The maximum velocity error which can be caused by an incorrect value is 0.5
km/s. The default value for the attribute is zero.
TimeFrame
Together with the ObsLon
attribute, it is used when converting between certain time scales (TDB, TCB, LMST, LAST)