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Subroutine: IRCO_PRECESS

Purpose: precess a coordinate system

Category WORLD COORDINATES, IRAS

File: irco.shl

Author: Do Kester

Person resp.: Do Kester

Address: guspace!do or rugfx4!do (uucp)

Use: call irco_precess(
refcoor I integer
year I real
newcoor I/O integer )

refcoor reference coordinate system
year year to precess to
newcoor input: 0 => output: free coordinate number
otherwise output = input
Description:
Precession can be applied to the coordinate systems Equatorial
and Ecliptic (numbers 1 and 3). YEAR is the year to precess
to e.g. 1950.0
The name of the system will be adjusted to the new epoch.

If NEWCOOR equals REFCOOR all transformation matrices
that referred to REFCOOR will be precessed. If NEWCOOR
is 0 upon entry, a free coordinate number will be returned,
or 0 if none is available any more.
Upon output NEWCOOR contains the number of the precessed system.

Note that if NEWCOOR equals REFCOOR subsequent precessions
will be with respect to the last result and more importantly
errors will accumulate in the process.

The connection to coordinate system nr 1 is always made, so that
all connections with other systems will be present in one or
two steps.

Reference: Lieske etal. Astron & Astrophys. (1977) 58 p.1 - 16.

Externals:

Updates: 5 jan 1990 DK, documentation only
17 DEC 1990 DK, make always connection with system nr 1