Previous: FIND /MASK
LAS\FIND /POSITION A0 D0 GALACTIC|EQUATORIAL [Equinox]
Selection observations according to their absolute position. A0 and D0
are sexagesimal strings (degrees, or hour angle for A0 in case of equa-
torial coordinates). The coordinate system (and its equinox for equato-
rial system) must be provided as third (and fourth) argument to the op-
In practice, the option converts (if they are different) the given coor-
dinates to the system used by the observation currently considered (e.g.
galactic to equatorial 2000). Then it translates the absolute position
to relative position. Finally, it compares the offset position of the
observation to this computed reference. SET MATCH is used as tolerance
(same as FIND /OFFSET). These operations are repeated for all observa-
tions in the file.
Beware this option is less efficient than its equivalent FIND /OFFSET
(which uses only index elements). When considering absolute coordinates,
the whole position section must be read for each observations. As the
Class Data Format does not enforce consistency of the reference posi-
tions of all the observations, all the conversions described above must
be repeated for all observations. But if you know your file is consis-
tent, FIND /OFFSET will always be faster for the same result. For exam-
ple, prefer FIND /OFFSET 0 0 instead of FIND /POSITION to select the
spectra near the reference position.