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ObsAlt - The geodetic altitude of the observer

Description:
This attribute specifies the geodetic altitude of the observer, in metres, relative to the IAU 1976 reference ellipsoid. 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.
Type:
String.
Class Applicability:
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)


next up previous 264
Next: ObsLat - The geodetic latitude of the observer
Up: AST Attribute Descriptions
Previous: ObjSize - The in-memory size of the Object

AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 211
R.F. Warren-Smith & D.S. Berry
25th February 2013
E-mail:starlink@jiscmail.ac.uk

Copyright (C) 2014 Science \& Technology Facilities Council