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100 lines
2.4 KiB
Fortran
100 lines
2.4 KiB
Fortran
SUBROUTINE sla_DC62S (V, A, B, R, AD, BD, RD)
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*+
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* - - - - - -
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* D C 6 2 S
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* - - - - - -
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*
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* Conversion of position & velocity in Cartesian coordinates
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* to spherical coordinates (double precision)
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*
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* Given:
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* V d(6) Cartesian position & velocity vector
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*
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* Returned:
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* A d longitude (radians)
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* B d latitude (radians)
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* R d radial coordinate
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* AD d longitude derivative (radians per unit time)
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* BD d latitude derivative (radians per unit time)
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* RD d radial derivative
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*
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* P.T.Wallace Starlink 28 April 1996
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*
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* Copyright (C) 1996 Rutherford Appleton Laboratory
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*
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* License:
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (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 useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* 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 (see SLA_CONDITIONS); if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place, Suite 330,
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* Boston, MA 02111-1307 USA
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*
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*-
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IMPLICIT NONE
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DOUBLE PRECISION V(6),A,B,R,AD,BD,RD
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DOUBLE PRECISION X,Y,Z,XD,YD,ZD,RXY2,RXY,R2,XYP
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* Components of position/velocity vector
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X=V(1)
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Y=V(2)
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Z=V(3)
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XD=V(4)
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YD=V(5)
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ZD=V(6)
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* Component of R in XY plane squared
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RXY2=X*X+Y*Y
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* Modulus squared
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R2=RXY2+Z*Z
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* Protection against null vector
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IF (R2.EQ.0D0) THEN
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X=XD
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Y=YD
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Z=ZD
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RXY2=X*X+Y*Y
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R2=RXY2+Z*Z
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END IF
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* Position and velocity in spherical coordinates
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RXY=SQRT(RXY2)
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XYP=X*XD+Y*YD
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IF (RXY2.NE.0D0) THEN
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A=ATAN2(Y,X)
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B=ATAN2(Z,RXY)
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AD=(X*YD-Y*XD)/RXY2
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BD=(ZD*RXY2-Z*XYP)/(R2*RXY)
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ELSE
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A=0D0
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IF (Z.NE.0D0) THEN
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B=ATAN2(Z,RXY)
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ELSE
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B=0D0
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END IF
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AD=0D0
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BD=0D0
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END IF
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R=SQRT(R2)
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IF (R.NE.0D0) THEN
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RD=(XYP+Z*ZD)/R
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ELSE
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RD=0D0
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END IF
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END
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