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Index Page latcyl_c

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Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries

#### Procedure

       latcyl_c ( Latitudinal to cylindrical coordinates )

       void latcyl_c ( SpiceDouble    radius,
                       SpiceDouble    lon,
                       SpiceDouble    lat,
                       SpiceDouble *  r,
                       SpiceDouble *  clon,
                       SpiceDouble *  z )

#### Abstract

       Convert from latitudinal coordinates to cylindrical coordinates.

#### Required_Reading

       None.

#### Keywords

       CONVERSION
       COORDINATES

#### Brief_I/O

       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       radius     I   Distance of a point from the origin.
       lon        I   Angle of the point from the XZ plane in radians.
       lat        I   Angle of the point from the XY plane in radians.
       r          O   Distance of the point from the z axis.
       clon       O   Angle of the point from the XZ plane in radians.
       z          O   Height of the point above the XY plane.

#### Detailed_Input

       radius      is the distance of a point from the origin.

       lon         is the angle of the point from the XZ plane in radians.

       lat         is the angle of the point from the XY plane in radians.

#### Detailed_Output

       r           is the distance of the point from the z axis.

       clon        is the angle of the point from the XZ plane in radians.
                   `clon' is set equal to `lon'.

       z           is the height of the point above the XY plane.

#### Parameters

       None.

#### Exceptions

       Error free.

#### Files

       None.

#### Particulars

       This routine returns the cylindrical coordinates of a point
       whose position is input in latitudinal coordinates.

       Latitudinal coordinates are defined by a distance from a central
       reference point, an angle from a reference meridian, and an angle
       above the equator of a sphere centered at the central reference
       point.

#### 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 latitudinal coordinates of the position of the Moon
          as seen from the Earth, and convert them to cylindrical and
          rectangular coordinates.

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

             KPL/MK

             File name: latcyl_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 latcyl_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
          {

             /.
             Local variables
             ./
             SpiceDouble          clon;
             SpiceDouble          et;
             SpiceDouble          lat;
             SpiceDouble          lon;
             SpiceDouble          lt;
             SpiceDouble          pos    [3];
             SpiceDouble          radius;
             SpiceDouble          rectan [3];
             SpiceDouble          r;
             SpiceDouble          z;

             /.
             Load SPK and LSK kernels, use a meta kernel for
             convenience.
             ./
             furnsh_c ( "latcyl_ex1.tm" );

             /.
             Look up the geometric state of the Moon as seen from
             the Earth at 2017 Mar 20, relative to the J2000
             reference frame.
             ./
             str2et_c ( "2017 Mar 20", &et );

             spkpos_c ( "Moon", et, "J2000", "NONE", "Earth", pos, &lt );

             /.
             Convert the position vector `pos' to latitudinal
             coordinates.
             ./
             reclat_c ( pos, &radius, &lon, &lat );

             /.
             Convert the latitudinal coordinates to cylindrical.
             ./
             latcyl_c ( radius, lon, lat, &r, &clon, &z );

             /.
             Convert the cylindrical coordinates to rectangular.
             ./
             cylrec_c ( r, clon, z, rectan );

             printf( " \n" );
             printf( "Original rectangular coordinates:\n" );
             printf( " \n" );
             printf( " X          (km):  %19.8f\n", pos[0] );
             printf( " Y          (km):  %19.8f\n", pos[1] );
             printf( " Z          (km):  %19.8f\n", pos[2] );
             printf( " \n" );
             printf( "Latitudinal coordinates:\n" );
             printf( " \n" );
             printf( " Radius     (km):  %19.8f\n", radius );
             printf( " Longitude (deg):  %19.8f\n", lon*dpr_c ( ) );
             printf( " Latitude  (deg):  %19.8f\n", lat*dpr_c ( ) );
             printf( " \n" );
             printf( "Cylindrical coordinates:\n" );
             printf( " \n" );
             printf( " Radius     (km):  %19.8f\n", r );
             printf( " Longitude (deg):  %19.8f\n", clon*dpr_c ( ) );
             printf( " Z          (km):  %19.8f\n", z );
             printf( " \n" );
             printf( "Rectangular coordinates from cylrec_c:\n" );
             printf( " \n" );
             printf( " X          (km):  %19.8f\n", rectan[0] );
             printf( " Y          (km):  %19.8f\n", rectan[1] );
             printf( " Z          (km):  %19.8f\n", rectan[2] );
             printf( " \n" );

             return ( 0 );
          }

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

          Original rectangular coordinates:

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

          Latitudinal coordinates:

           Radius     (km):      403626.33912495
           Longitude (deg):         -98.34959789
           Latitude  (deg):         -18.26566077

          Cylindrical coordinates:

           Radius     (km):      383289.01777726
           Longitude (deg):         -98.34959789
           Z          (km):     -126505.93063865

          Rectangular coordinates from cylrec_c:

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

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

          Corresponding latitudinal and cylindrical coordinates are
          listed to three decimal places. Input and output angles are
          in degrees.

          Example code begins here.

          /.
             Program latcyl_ex2
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
          {

             /.
             Local parameters.
             ./
             #define NREC         11

             /.
             Local variables.
             ./
             SpiceDouble          clon;
             SpiceDouble          r;
             SpiceDouble          rlat;
             SpiceDouble          rlon;
             SpiceDouble          z;

             SpiceInt             i;

             /.
             Define the input latitudinal coordinates. Angles in degrees.
             ./

             SpiceDouble          radius [NREC] = { 0.0,  1.0,     1.0,
                                                    1.0,  1.4142,  1.0,
                                                    1.0,  1.0,     1.4142,
                                                    1.0,  0.0             };

             SpiceDouble          lon    [NREC] = {   0.0,    0.0,   90.0,
                                                      0.0,  180.0,  -90.0,
                                                      0.0,   45.0,  180.0,
                                                    180.0,    33.0        };

             SpiceDouble          lat    [NREC] = {  90.0,   0.0,    0.0,
                                                     90.0,  45.0,    0.0,
                                                    -90.0,   0.0,  -45.0,
                                                     90.0,   0.0         };

             /.
             Print the banner.
             ./
             printf( "  radius    lon      lat       r       clon      z   \n" );
             printf( " -------  -------  -------  -------  -------  -------\n" );

             /.
             Do the conversion. Output angles in degrees.
             ./
             for ( i = 0; i < NREC; i++ )
             {

                rlon = lon[i] * rpd_c ( );
                rlat = lat[i] * rpd_c ( );

                latcyl_c ( radius[i], rlon, rlat, &r, &clon, &z );

                printf( "%8.3f %8.3f %8.3f ", radius[i], lon[i], lat[i] );
                printf( "%8.3f %8.3f %8.3f\n", r, clon * dpr_c ( ), z );

             }

             return ( 0 );
          }

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

            radius    lon      lat       r       clon      z
           -------  -------  -------  -------  -------  -------
             0.000    0.000   90.000    0.000    0.000    0.000
             1.000    0.000    0.000    1.000    0.000    0.000
             1.000   90.000    0.000    1.000   90.000    0.000
             1.000    0.000   90.000    0.000    0.000    1.000
             1.414  180.000   45.000    1.000  180.000    1.000
             1.000  -90.000    0.000    1.000  -90.000    0.000
             1.000    0.000  -90.000    0.000    0.000   -1.000
             1.000   45.000    0.000    1.000   45.000    0.000
             1.414  180.000  -45.000    1.000  180.000   -1.000
             1.000  180.000   90.000    0.000  180.000    1.000
             0.000   33.000    0.000    0.000   33.000    0.000

       3) Other than the obvious conversion between coordinate systems
          this routine could be used to obtain the axial projection
          from a sphere to a cylinder about the z-axis that contains
          the equator of the sphere.

          Such a projection is valuable because it preserves the
          areas between regions on the sphere and their projections to
          the cylinder.

          Example code begins here.

          /.
             Program latcyl_ex3
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
          {

             /.
             Local variables
             ./
             SpiceDouble          clon;
             SpiceDouble          lat;
             SpiceDouble          lon;
             SpiceDouble          radius;
             SpiceDouble          r;
             SpiceDouble          z;

             /.
             Define the point whose projection is to be
             computed.
             ./
             radius =  100.0;
             lon    =   45.0  * rpd_c ( );
             lat    =  -12.5 * rpd_c ( );

             /.
             Convert the latitudinal coordinates to cylindrical.
             ./
             latcyl_c ( radius, lon, lat, &r, &clon, &z );

             printf( "Coordinates of the projected point on cylinder:\n" );
             printf( " \n" );
             printf( " Radius     (km):  %22.11f\n", r );
             printf( " Longitude (deg):  %22.11f\n", clon*dpr_c ( ) );
             printf( " Z          (km):  %22.11f\n", z );

             return ( 0 );
          }

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

          Coordinates of the projected point on cylinder:

           Radius     (km):          97.62960071199
           Longitude (deg):          45.00000000000
           Z          (km):         -21.64396139381

#### 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

       -CSPICE Version 1.1.0, 04-JUL-2021 (JDR)

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

           Changed the input argument name "lonc" to "clon" for consistency
           with other routines.

       -CSPICE Version 1.0.1, 26-JUL-2016 (BVS)

           Minor headers edits.

       -CSPICE Version 1.0.0, 08-FEB-1998 (EDW) (WLT)

#### Index_Entries

       latitudinal to cylindrical coordinates

#### Link to routine latcyl_c source file latcyl_c.c

    Fri Dec 31 18:41:08 2021