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cspice_latrec

Table of contents
Abstract
I/O
Parameters
Examples
Particulars
Exceptions
Files
Restrictions
Required_Reading
Literature_References
Author_and_Institution
Version
Index_Entries


Abstract


   CSPICE_LATREC converts latitudinal coordinates to rectangular
   (Cartesian) coordinates.

I/O


   Given:

      radius   the distance of a point from the origin, or an N-vector of
               distances.

               help, radius
                  DOUBLE = Scalar   or   DOUBLE = Array[N]

      lon      the longitude of the input point, or an N-vector of
               longitudes.

               help, lon
                  DOUBLE = Scalar   or   DOUBLE = Array[N]

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

               Longitude is measured in radians. On input, the
               range of longitude is unrestricted.

      lat      the latitude of the input point, or an N-vector of
               latitudes.

               help, lat
                  DOUBLE = Scalar   or   DOUBLE = Array[N]

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

               Latitude is measured in radians. On input, the range
               of latitude is unrestricted.

   the call:

      cspice_latrec, radius, lon, lat, rectan

   returns:

      rectan   the rectangular coordinates of the input point, or an N-vector
               of coordinates.

               help, rectan
                  DOUBLE = Array[3]   or   DOUBLE = Array[3,N]

               `rectan' is a 3-vector.

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

Parameters


   None.

Examples


   Any numerical results shown for these examples may differ between
   platforms as the results depend on the SPICE kernels used as input
   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: latrec_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.


      PRO latrec_ex1

         ;;
         ;; Load SPK and LSK kernels, use a meta kernel for
         ;; convenience.
         ;;
         cspice_furnsh, 'latrec_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.
         ;;
         cspice_str2et, '2017 Mar 20', et

         cspice_spkpos, 'Moon', et, 'J2000', 'NONE', 'Earth', pos, ltime

         ;;
         ;; Convert the position vector `pos' to latitudinal
         ;; coordinates.
         ;;
         cspice_reclat, pos, radius, lon, lat

         ;;
         ;; Convert the latitudinal to rectangular coordinates.
         ;;
         cspice_latrec, radius, lon, lat, rectan

         print, ' '
         print, 'Original rectangular coordinates:'
         print, ' '
         print, format='(A,F20.8)', ' X          (km): ', pos[0]
         print, format='(A,F20.8)', ' Y          (km): ', pos[1]
         print, format='(A,F20.8)', ' Z          (km): ', pos[2]
         print, ' '
         print, 'Latitudinal coordinates:'
         print, ' '
         print, format='(A,F20.8)', ' Radius     (km): ', radius
         print, format='(A,F20.8)', ' Longitude (deg): ', lon*cspice_dpr( )
         print, format='(A,F20.8)', ' Latitude  (deg): ', lat*cspice_dpr( )
         print, ' '
         print, 'Rectangular coordinates from cspice_latrec:'
         print, ' '
         print, format='(A,F20.8)', ' X          (km): ', rectan[0]
         print, format='(A,F20.8)', ' Y          (km): ', rectan[1]
         print, format='(A,F20.8)', ' Z          (km): ', rectan[2]
         print, ' '

      END


      When this program was executed on a Mac/Intel/IDL8.x/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 cspice_latrec:

       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 rectangular coordinates.

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


      Example code begins here.


      PRO latrec_ex2

         ;;
         ;; Define eleven sets of latitude coordinates, `longitude'
         ;; and `latitude' expressed in degrees.
         ;;
         radius   = [ 0d, 1d, 1d , 1d , 1d  ,   1d, $
                      1d, 1.4142d, 1.4142d, 1.4142d, 1.732d   ]

         longitude= [ 0d, 0d, 90d, 0d , 180d, -90d, $
                      0d, 45d    , 0d     , 90d    , 45d      ]

         latitude = [ 0d, 0d, 0d , 90d, 0d  ,   0d, $
                    -90d, 0d     , 45d    , 45d    , 35.2643d ]

         lon_rad = longitude * cspice_rpd()
         lat_rad = latitude  * cspice_rpd()

         ;;
         ;; Convert the coordinates from latitudinal to rectangular.
         ;;
         cspice_latrec, radius, lon_rad, lat_rad, rectan

         ;;
         ;; Print a header for the data output.
         ;;
         print, '   radius    lon       lat ', $
                '  rect[0]  rect[1]  rect[2]'
         print, '  -------  -------  -------', $
                '  -------  -------  -------'

         ;;
         ;; Load the data for easy output.
         ;;
         output      = dblarr( 6, 11 )

         output[0,*] = radius
         output[1,*] = longitude
         output[2,*] = latitude
         output[3,*] = rectan[0,*]
         output[4,*] = rectan[1,*]
         output[5,*] = rectan[2,*]

         ;;
         ;; Output the coordinate table.
         ;;
         print, FORMAT='(6D9.3)', output

      END


      When this program was executed on a Mac/Intel/IDL8.x/64-bit
      platform, the output was:


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


Particulars


   This routine returns the rectangular 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.

Exceptions


   1)  If any of the input arguments, `radius', `lon' or `lat', is
       undefined, an error is signaled by the IDL error handling
       system.

   2)  If any of the input arguments, `radius', `lon' or `lat', is
       not of the expected type, or it does not have the expected
       dimensions and size, an error is signaled by the Icy
       interface.

   3)  If the input vectorizable arguments `radius', `lon' and `lat'
       do not have the same measure of vectorization (N), an error is
       signaled by the Icy interface.

   4)  If the output argument `rectan' is not a named variable, an
       error is signaled by the Icy interface.

Files


   None.

Restrictions


   None.

Required_Reading


   ICY.REQ

Literature_References


   None.

Author_and_Institution


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

Version


   -Icy Version 1.2.0, 13-AUG-2021 (JDR)

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

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

       Added -Parameters, -Exceptions, -Files, -Restrictions,
       -Literature_References and -Author_and_Institution sections, and
       completed -Particulars section.

       Removed reference to the routine's corresponding CSPICE header from
       -Abstract section.

       Added arguments' type and size information in the -I/O section.

   -Icy Version 1.1.1, 05-FEB-2008 (EDW)

       Edited -I/O section, replaced comment

          "returns with the same order"

       with

          "returns with the same measure of vectorization"

   -Icy Version 1.1.0, 12-SEP-2004 (EDW)

       Added capability to process vectors 'radius',
       'longitude', and 'latitude' as input,
       returning array 'rectan' on output.

   -Icy Version 1.0.0, 16-JUN-2003 (EDW)

Index_Entries


   latitudinal to rectangular coordinates



Fri Dec 31 18:43:05 2021