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palRverot.c
Go to the documentation of this file.
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/*
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*+
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* Name:
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* palRverot
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* Purpose:
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* Velocity component in a given direction due to Earth rotation
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* Language:
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* Starlink ANSI C
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* Type of Module:
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* Library routine
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* Invocation:
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* double palRverot ( double phi, double ra, double da, double st );
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* Arguments:
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* phi = double (Given)
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* latitude of observing station (geodetic) (radians)
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* ra = double (Given)
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* apparent RA (radians)
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* da = double (Given)
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* apparent Dec (radians)
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* st = double (Given)
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* Local apparent sidereal time.
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* Returned Value:
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* palRverot = double
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* Component of Earth rotation in direction RA,DA (km/s).
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* The result is +ve when the observatory is receding from the
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* given point on the sky.
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* Description:
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* Calculate the velocity component in a given direction due to Earth
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* rotation.
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*
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* The simple algorithm used assumes a spherical Earth, of
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* a radius chosen to give results accurate to about 0.0005 km/s
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* for observing stations at typical latitudes and heights. For
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* applications requiring greater precision, use the routine
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* palPvobs.
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* Authors:
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* PTW: Patrick T. Wallace
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* TIMJ: Tim Jenness (JAC, Hawaii)
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* {enter_new_authors_here}
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* History:
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* 2012-03-02 (TIMJ):
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* Initial version
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* Adapted with permission from the Fortran SLALIB library.
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* {enter_further_changes_here}
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* Copyright:
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* Copyright (C) 1995 Rutherford Appleton Laboratory
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* Copyright (C) 2012 Science and Technology Facilities Council.
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* All Rights Reserved.
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* Licence:
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 3 of
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* the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be
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* useful, but WITHOUT ANY WARRANTY; without even the implied
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* warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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* PURPOSE. See the GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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* MA 02110-1301, USA.
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* Bugs:
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* {note_any_bugs_here}
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*-
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*/
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#include "
pal.h
"
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#include <math.h>
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double
palRverot
(
double
phi,
double
ra,
double
da,
double
st ) {
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/* Nominal mean sidereal speed of Earth equator in km/s (the actual
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* value is about 0.4651) */
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const
double
espeed = 0.4655;
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return
espeed * cos(phi) * sin(st-ra) * cos(da);
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}
pal.h
palRverot
double palRverot(double phi, double ra, double da, double st)
Definition:
palRverot.c:85
pal
palRverot.c
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