georec_c

Index Page georec_c
A B C D E F G H I J K L M N O P Q R S T U V W X
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
       void georec_c ( SpiceDouble lon,
                       SpiceDouble lat,
                       SpiceDouble alt,
                       SpiceDouble re,
                       SpiceDouble f,
                       SpiceDouble rectan[3] )
#### Abstract
       Convert geodetic coordinates to rectangular coordinates.
#### Required_Reading
       None.
#### Keywords
       CONVERSION,  COORDINATES
#### Brief_I/O
       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       lon        I   Geodetic longitude of point (radians).
       lat        I   Geodetic latitude  of point (radians).
       alt        I   Altitude of point above the reference spheroid.
       re         I   Equatorial radius of the reference spheroid.
       f          I   Flattening coefficient.
       rectan     O   Rectangular coordinates of point.
#### Detailed_Input
       lon        Geodetic longitude of the input point.  This is the
                  angle between the prime meridian and the meridian
                  containing `rectan'.  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        Geodetic latitude of the input point.  For a point P on
                  the reference spheroid, this is the angle between the XY
                  plane and the outward normal vector at P. For a point P
                  not on the reference spheroid, the geodetic latitude is
                  that of the closest point to P on the spheroid.

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

       alt        Altitude of point above the reference spheroid.

       re         Equatorial radius of a reference spheroid.  This spheroid
                  is a volume of revolution:  its horizontal cross sections
                  are circular.  The shape of the spheroid is defined by
                  an equatorial radius `re' and a polar radius `rp'.

       f          Flattening coefficient = (re-rp) / re,  where `rp' is
                  the polar radius of the spheroid.
#### Detailed_Output
       rectan     Rectangular coordinates of the input point.

                  The units associated with `rectan' are those associated
                  with the input `alt'.
#### Parameters
       None.
#### Exceptions
       1) If the equatorial radius is less than or equal to zero,
          the error SPICE(VALUEOUTOFRANGE) is signaled.

       2) If the flattening coefficient is greater than or equal to
          one, the error SPICE(VALUEOUTOFRANGE) is signaled.
#### Files
       None.
#### Particulars
       Given the geodetic coordinates of a point, and the constants
       describing the reference spheroid,  this routine returns the
       bodyfixed rectangular coordinates of the point.  The bodyfixed
       rectangular frame is that having the x-axis pass through the 0
       degree latitude 0 degree longitude point.  The y-axis passes through
       the 0 degree latitude 90 degree longitude.  The z-axis passes
       through the 90 degree latitude point.  For some bodies this
       coordinate system may not be a right-handed coordinate system.
#### Examples
       This routine can be used to convert body fixed geodetic
       coordinates (such as the used for United States Geological
       Survey topographic maps) to bodyfixed rectangular coordinates
       such as the Satellite Tracking and Data Network of 1973.

       The code would look something like this

          /.
          Using the equatorial radius of the Clark66 spheroid
          (CLARKR = 6378.2064 km) and the Clark 66 flattening
          factor (CLARKF = 1.0 / 294.9787 ) convert to
          body fixed rectangular coordinates.
          ./

          georec_c ( lon, lat, alt, CLARKR, CLARKF, x );

          /.
          Add the North American Datum of 1927 to STDN 73 center
          offset
          ./

          vadd_c  ( x, offset, stdnx );

       Below are two tables.

       Listed in the first table (under lon, lat, and alt ) are
       geodetic coordinate triples that approximately represent points
       whose rectangular coordinates are taken from the set {-1, 0, 1}.
       (Angular quantities are given in degrees.)

       The results of the code fragment

          /.
          Convert the angular quantities to degrees
          ./
          lat = lat * rpd_c();
          lon = lon * rpd_c();

          georec_c ( lon, lat, alt, CLARKR, CLARKF, x );

       are listed in the second parallel table under x[0], x[1] and x[2].

         lon       lat        alt            x[0]       x[1]     x[2]
         ------------------------------      --------------------------
         0.0000    90.0000   -6356.5838      0.0000     0.0000   0.0000
         0.0000     0.0000   -6377.2063      1.0000     0.0000   0.0000
        90.0000     0.0000   -6377.2063      0.0000     1.0000   0.0000
         0.0000    90.0000   -6355.5838      0.0000     0.0000   1.0000
       180.0000     0.0000   -6377.2063     -1.0000     0.0000   0.0000
       -90.0000     0.0000   -6377.2063      0.0000    -1.0000   0.0000
         0.0000   -90.0000   -6355.5838      0.0000     0.0000  -1.0000
        45.0000     0.0000   -6376.7921      1.0000     1.0000   0.0000
         0.0000    88.7070   -6355.5725      1.0000     0.0000   1.0000
        90.0000    88.7070   -6355.5725      0.0000     1.0000   1.0000
        45.0000    88.1713   -6355.5612      1.0000     1.0000   1.0000
#### Restrictions
       None.
#### Literature_References
       See FUNDAMENTALS OF ASTRODYNAMICS, Bate, Mueller, White
       published by Dover for a description of geodetic coordinates.
#### Author_and_Institution
       C.H. Acton      (JPL)
       N.J. Bachman    (JPL)
       H.A. Neilan     (JPL)
       W.L. Taber      (JPL)
       E.D. Wright     (JPL)
#### Version
       -CSPICE Version 1.0.2, 30-JUL-2003 (NJB)

          Various header corrections were made.

       -CSPICE Version 1.0.1, 11-JAN-2003   (EDW)

           Removed a spurious non-printing character.

       -CSPICE Version 1.0.0, 08-FEB-1998   (EDW)
#### Index_Entries
       geodetic to rectangular coordinates
#### Link to routine georec_c source file georec_c.c

    Thu Apr 16 08:58:09 2009