Procedure

     RECCYL ( Rectangular to cylindrical coordinates )

     SUBROUTINE RECCYL ( RECTAN, R, CLON, Z )

Abstract

     Convert from rectangular to cylindrical coordinates.

Required_Reading

     None.

Keywords

     CONVERSION
     COORDINATES

Declarations

     IMPLICIT NONE

     DOUBLE PRECISION RECTAN(3)
     DOUBLE PRECISION R
     DOUBLE PRECISION CLON
     DOUBLE PRECISION Z

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  -------------------------------------------------
     RECTAN     I   Rectangular coordinates of a point.
     R          O   Distance of the point from Z axis.
     CLON       O   Angle (radians) of the point from XZ plane
     Z          O   Height of the point above XY plane.

Detailed_Input

     RECTAN   are the rectangular coordinates of the point of
              interest.

Detailed_Output

     R        is the distance of the point of interest from Z-axis.

     CLON     is the cylindrical angle (in radians) of the point of
              interest from XZ plane. The CLON range is [0, 2pi].

     Z        is the height of the point above XY plane.

Parameters

     None.

Exceptions

     Error free.

Files

     None.

Particulars

     This routine transforms the coordinates of a point from
     rectangular to cylindrical coordinates.

Examples

     The numerical results shown for these examples may differ across
     platforms. The results depend on the SPICE kernels used as
     input, the compiler and supporting libraries, and the machine
     specific arithmetic implementation.

     1) Compute the cylindrical coordinates of the position of the Moon
        as seen from the Earth, and convert them to rectangular
        coordinates.

        Use the meta-kernel shown below to load the required SPICE
        kernels.


           KPL/MK

           File name: reccyl_ex1.tm

           This meta-kernel is intended to support operation of SPICE
           example programs. The kernels shown here should not be
           assumed to contain adequate or correct versions of data
           required by SPICE-based user applications.

           In order for an application to use this meta-kernel, the
           kernels referenced here must be present in the user's
           current working directory.

           The names and contents of the kernels referenced
           by this meta-kernel are as follows:

              File name                     Contents
              ---------                     --------
              de421.bsp                     Planetary ephemeris
              naif0012.tls                  Leapseconds


           \begindata

              KERNELS_TO_LOAD = ( 'de421.bsp',
                                  'naif0012.tls'  )

           \begintext

           End of meta-kernel


        Example code begins here.


              PROGRAM RECCYL_EX1
              IMPLICIT NONE

        C
        C     SPICELIB functions
        C
              DOUBLE PRECISION      DPR

        C
        C     Local parameters
        C
              CHARACTER*(*)         FMT1
              PARAMETER           ( FMT1 = '(A,F20.8)' )

        C
        C     Local variables
        C
              DOUBLE PRECISION      CLON
              DOUBLE PRECISION      ET
              DOUBLE PRECISION      LT
              DOUBLE PRECISION      POS    ( 3 )
              DOUBLE PRECISION      RECTAN ( 3 )
              DOUBLE PRECISION      R
              DOUBLE PRECISION      Z

        C
        C     Load SPK and LSK kernels, use a meta kernel for
        C     convenience.
        C
              CALL FURNSH ( 'reccyl_ex1.tm' )

        C
        C     Look up the geometric state of the Moon as seen from
        C     the Earth at 2017 Mar 20, relative to the J2000
        C     reference frame.
        C
              CALL STR2ET ( '2017 Mar 20', ET )

              CALL SPKPOS ( 'Moon',  ET,  'J2000', 'NONE',
             .              'Earth', POS, LT               )

        C
        C     Convert the position vector POS to cylindrical
        C     coordinates.
        C
              CALL RECCYL ( POS, R, CLON, Z )

        C
        C     Convert the cylindrical to rectangular coordinates.
        C

              CALL CYLREC ( R, CLON, Z, RECTAN )

              WRITE(*,*) ' '
              WRITE(*,*) 'Original rectangular coordinates:'
              WRITE(*,*) ' '
              WRITE(*,FMT1) '  X          (km): ', POS(1)
              WRITE(*,FMT1) '  Y          (km): ', POS(2)
              WRITE(*,FMT1) '  Z          (km): ', POS(3)
              WRITE(*,*) ' '
              WRITE(*,*) 'Cylindrical coordinates:'
              WRITE(*,*) ' '
              WRITE(*,FMT1) '  Radius     (km): ', R
              WRITE(*,FMT1) '  Longitude (deg): ', CLON*DPR()
              WRITE(*,FMT1) '  Z          (km): ', Z
              WRITE(*,*) ' '
              WRITE(*,*) 'Rectangular coordinates from CYLREC:'
              WRITE(*,*) ' '
              WRITE(*,FMT1) '  X          (km): ', RECTAN(1)
              WRITE(*,FMT1) '  Y          (km): ', RECTAN(2)
              WRITE(*,FMT1) '  Z          (km): ', RECTAN(3)
              WRITE(*,*) ' '

              END


        When this program was executed on a Mac/Intel/gfortran/64-bit
        platform, the output was:


         Original rectangular coordinates:

          X          (km):      -55658.44323296
          Y          (km):     -379226.32931475
          Z          (km):     -126505.93063865

         Cylindrical coordinates:

          Radius     (km):      383289.01777726
          Longitude (deg):         261.65040211
          Z          (km):     -126505.93063865

         Rectangular coordinates from CYLREC:

          X          (km):      -55658.44323296
          Y          (km):     -379226.32931475
          Z          (km):     -126505.93063865


     2) Create a table showing a variety of rectangular coordinates
        and the corresponding cylindrical coordinates.

        Corresponding rectangular and cylindrical coordinates are
        listed to three decimal places. Output angles are in degrees.


        Example code begins here.


              PROGRAM RECCYL_EX2
              IMPLICIT NONE

        C
        C     SPICELIB functions
        C
              DOUBLE PRECISION      DPR

        C
        C     Local parameters.
        C
              INTEGER               NREC
              PARAMETER           ( NREC = 11 )

        C
        C     Local variables.
        C
              DOUBLE PRECISION      CLON
              DOUBLE PRECISION      R
              DOUBLE PRECISION      RECTAN ( 3, NREC )
              DOUBLE PRECISION      Z

              INTEGER               I
              INTEGER               J

        C
        C     Define the input rectangular coordinates.
        C
              DATA                 RECTAN /
             .                  0.D0,         0.D0,         0.D0,
             .                  1.D0,         0.D0,         0.D0,
             .                  0.D0,         1.D0,         0.D0,
             .                  0.D0,         0.D0,         1.D0,
             .                 -1.D0,         0.D0,         0.D0,
             .                  0.D0,        -1.D0,         0.D0,
             .                  0.D0,         0.D0,        -1.D0,
             .                  1.D0,         1.D0,         0.D0,
             .                  1.D0,         0.D0,         1.D0,
             .                  0.D0,         1.D0,         1.D0,
             .                  1.D0,         1.D0,         1.D0  /

        C
        C     Print the banner.
        C
              WRITE(*,*) ' RECT(1)  RECT(2)  RECT(3) '
             . //        '    R       CLON      Z'
              WRITE(*,*) ' -------  -------  ------- '
             . //        ' -------  -------  ------- '

        C
        C     Do the conversion. Output angles in degrees.
        C
              DO I = 1, NREC

                 CALL RECCYL( RECTAN(1,I), R, CLON, Z )

                 WRITE (*,'(6F9.3)') ( RECTAN(J,I), J=1,3 ),
             .                         R, CLON * DPR(), Z

              END DO

              END


        When this program was executed on a Mac/Intel/gfortran/64-bit
        platform, the output was:


          RECT(1)  RECT(2)  RECT(3)     R       CLON      Z
          -------  -------  -------  -------  -------  -------
            0.000    0.000    0.000    0.000    0.000    0.000
            1.000    0.000    0.000    1.000    0.000    0.000
            0.000    1.000    0.000    1.000   90.000    0.000
            0.000    0.000    1.000    0.000    0.000    1.000
           -1.000    0.000    0.000    1.000  180.000    0.000
            0.000   -1.000    0.000    1.000  270.000    0.000
            0.000    0.000   -1.000    0.000    0.000   -1.000
            1.000    1.000    0.000    1.414   45.000    0.000
            1.000    0.000    1.000    1.000    0.000    1.000
            0.000    1.000    1.000    1.000   90.000    1.000
            1.000    1.000    1.000    1.414   45.000    1.000

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     J. Diaz del Rio    (ODC Space)
     B.V. Semenov       (JPL)
     W.L. Taber         (JPL)
     E.D. Wright        (JPL)

Version

    SPICELIB Version 1.1.0, 06-JUL-2021 (JDR)

        Changed the output argument name LONG to CLON for consistency
        with other routines.

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard.
        Added complete code examples.

    SPICELIB Version 1.0.3, 26-JUL-2016 (BVS)

        Minor headers edits.

    SPICELIB Version 1.0.2, 22-AUG-2001 (EDW)

        Corrected ENDIF to END IF. Obsolete $Revisions section
        deleted.

    SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.0, 31-JAN-1990 (WLT)