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Index Page reclat_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

       reclat_c ( Rectangular to latitudinal coordinates )

       void reclat_c ( ConstSpiceDouble    rectan[3],
                       SpiceDouble       * radius,
                       SpiceDouble       * lon,
                       SpiceDouble       * lat      )

#### Abstract

       Convert from rectangular coordinates to latitudinal coordinates.

#### Required_Reading

       None.

#### Keywords

       CONVERSION
       COORDINATES

#### Brief_I/O

       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       rectan     I   Rectangular coordinates of a point.
       radius     O   Distance of the point from the origin.
       lon        O   Longitude of the point in radians.
       lat        O   Latitude of the point in radians.

#### Detailed_Input

       rectan      are the rectangular coordinates of the input point.
                   `rectan' is a 3-vector.

#### Detailed_Output

       radius      is the distance of the point from the origin.

                   The units associated with `radius' are those
                   associated with the input `rectan'.

       lon         is the longitude of the input point. This is angle
                   between the prime meridian and the meridian
                   containing `rectan'. The direction of increasing
                   longitude is from the +X axis towards the +Y axis.

                   `lon' is output in radians. The range of `lon'
                   is [-pi, pi].

       lat         is the latitude of the input point. This is the angle
                   from the XY plane of the ray from the origin through the
                   point.

                   `lat' is output in radians. The range of `lat'
                   is [-pi/2, pi/2].

#### Parameters

       None.

#### Exceptions

       Error free.

       1)  If the X and Y components of `rectan' are both zero, the
           longitude is set to zero.

       2)  If `rectan' is the zero vector, longitude and latitude are
           both set to zero.

#### Files

       None.

#### Particulars

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

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

             KPL/MK

             File name: reclat_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 reclat_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
          {

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

             /.
             Load SPK and LSK kernels, use a meta kernel for
             convenience.
             ./
             furnsh_c ( "reclat_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 to rectangular coordinates.
             ./

             latrec_c ( radius, lon, lat, 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( "Rectangular coordinates from latrec_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

          Rectangular coordinates from latrec_c:

           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 latitudinal coordinates.

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

          Example code begins here.

          /.
             Program reclat_ex2
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
          {

             /.
             Local parameters.
             ./
             #define NREC         11

             /.
             Local variables.
             ./
             SpiceDouble          lat;
             SpiceDouble          lon;
             SpiceDouble          radius;

             SpiceInt             i;

             /.
             Define the input rectangular coordinates.
             ./
             SpiceDouble          rectan [NREC][3] = {
                                       { 0.0,         0.0,         0.0},
                                       { 1.0,         0.0,         0.0},
                                       { 0.0,         1.0,         0.0},
                                       { 0.0,         0.0,         1.0},
                                       {-1.0,         0.0,         0.0},
                                       { 0.0,        -1.0,         0.0},
                                       { 0.0,         0.0,        -1.0},
                                       { 1.0,         1.0,         0.0},
                                       { 1.0,         0.0,         1.0},
                                       { 0.0,         1.0,         1.0},
                                       { 1.0,         1.0,         1.0} };

             /.
             Print the banner.
             ./
             printf( " rect[0]  rect[1]  rect[2]   radius    lon      lat\n"   );
             printf( " -------  -------  -------  -------  -------  -------\n" );

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

                reclat_c ( rectan[i], &radius, &lon, &lat );

                printf( "%8.3f %8.3f %8.3f ", rectan[i][0], rectan[i][1],
                                              rectan[i][2]               );
                printf( "%8.3f %8.3f %8.3f\n", radius, lon * dpr_c ( ),
                                                       lat * dpr_c ( ) );

             }

             return ( 0 );
          }

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

           rect[0]  rect[1]  rect[2]   radius    lon      lat
           -------  -------  -------  -------  -------  -------
             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    1.000    0.000   90.000
            -1.000    0.000    0.000    1.000  180.000    0.000
             0.000   -1.000    0.000    1.000  -90.000    0.000
             0.000    0.000   -1.000    1.000    0.000  -90.000
             1.000    1.000    0.000    1.414   45.000    0.000
             1.000    0.000    1.000    1.414    0.000   45.000
             0.000    1.000    1.000    1.414   90.000   45.000
             1.000    1.000    1.000    1.732   45.000   35.264

#### Restrictions

       None.

#### Literature_References

       None.

#### Author_and_Institution

       N.J. Bachman        (JPL)
       J. Diaz del Rio     (ODC Space)
       E.D. Wright         (JPL)

#### Version

       -CSPICE Version 1.3.0, 10-AUG-2021 (JDR)

           Changed input argument names "longitude" and "latitude to "lon"
           and "lat" for consistency with other routines.

           Edited the header to comply with NAIF standard. Added
           complete code example based on existing example.

           Added -Particulars section.

       -CSPICE Version 1.2.1, 30-JUL-2003 (NJB)

           Various header changes were made to improve clarity. Some
           minor header corrections were made.

       -CSPICE Version 1.2.0, 28-AUG-2001 (NJB)

           Removed tab characters from source file. Now includes
           interface macro header SpiceZim.h.

       -CSPICE Version 1.1.0, 21-OCT-1998 (NJB)

           Made input vector const.

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

#### Index_Entries

       rectangular to latitudinal coordinates

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

    Fri Dec 31 18:41:11 2021