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Index Page convrt_c
Table of contents
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
       convrt_c ( Convert Units )

       void convrt_c ( SpiceDouble       x,
                       ConstSpiceChar  * in,
                       ConstSpiceChar  * out,
                       SpiceDouble     * y    )
#### Abstract
       Take a measurement X, the units associated with
       X, and units to which X should be converted; return Y ---
       the value of the measurement in the output units.
#### Required_Reading
       None.
#### Keywords
       CONVERSION
       UNITS
#### Brief_I/O
       VARIABLE  I/O  DESCRIPTION
       --------  ---  -------------------------------------------------
       x          I   Number representing a measurement in some units.
       in         I   The units in which x is measured.
       out        I   Desired units for the measurement.
       y          O   The measurement in the desired units.
#### Detailed_Input
       x           is a number representing a measurement in the units
                   specified by in.

       in          represents the units associated with a measurement x.
                   Acceptable units are:

                   Angles:                 "RADIANS"
                                           "DEGREES"
                                           "ARCMINUTES"
                                           "ARCSECONDS"
                                           "HOURANGLE"
                                           "MINUTEANGLE"
                                           "SECONDANGLE"

                   Metric Distances:       "METERS"
                                           "M"
                                           "KILOMETERS"
                                           "KM"
                                           "CENTIMETERS"
                                           "CM"
                                           "MILLIMETERS"
                                           "MM"

                   English Distances:      "FEET"
                                           "INCHES"
                                           "YARDS"
                                           "STATUTE_MILES"
                                           "NAUTICAL_MILES"

                   Astrometric Distances:  "AU"
                                           "PARSECS"
                                           "LIGHTSECS"
                                           "LIGHTYEARS" julian lightyears

                   Time:                   "SECONDS"
                                           "MINUTES"
                                           "HOURS"
                                           "DAYS"
                                           "JULIAN_YEARS"
                                           "TROPICAL_YEARS"
                                           "YEARS" (same as julian years)

                   The case of the string in is not significant.

       out         represents the units desired for the measurement x.
                   See the description of in.

                   The case of the string out is not significant.
#### Detailed_Output
       y           is the input measurement converted to the desired units.
#### Parameters
       None.
#### Exceptions
       1)  If the input units, output units, or both input and output
           units are not recognized, the error SPICE(UNITSNOTREC) is
           signaled by a routine in the call tree of this routine.

       2)  If the units being converted between are incompatible, the
           error SPICE(INCOMPATIBLEUNITS) is signaled by a routine in the
           call tree of this routine.

       3)  If any of the `in' or `out' input string pointers is null, the
           error SPICE(NULLPOINTER) is signaled.

       4)  If any of the `in' or `out' input strings has zero length, the
           error SPICE(EMPTYSTRING) is signaled.
#### Files
       None.
#### Particulars
       This routine converts a measurement x given in units specified by
       in to the equivalent value y in units specified by out.

       If a unit is not recognized, an error message is produced that
       indicates which one was not recognized.

       If input and output units are incompatible (for example angle
       and distance units) and error message will be produced stating
       the requested units and associated types.
#### Examples
       The numerical results shown for this example 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) Convert 300 miles (statute miles) to kilometers and determine
          the number of lightyears in a parsec.

          Example code begins here.

          /.
             Program convrt_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
          {

             /.
             Local variables.
             ./
             SpiceDouble               distsm;
             SpiceDouble               onpars;
             SpiceDouble               result;

             /.
             Convert 300 miles (statute miles) to kilometers.
             ./
             distsm = 300.0;
             convrt_c ( distsm, "statute_miles", "km", &result );
             printf ( "300 miles in km  : %16.6f\n",  result   );

             /.
             Determine the number of lightyears in a parsec.
             ./
             onpars = 1.0;
             convrt_c ( onpars, "PARSECS", "LIGHTYEARS", &result );
             printf ( "Lightyears/parsec: %16.6f\n",  result     );

             return ( 0 );
          }

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

          300 miles in km  :       482.803200
          Lightyears/parsec:         3.261564
#### Restrictions
       1)  This routine does not do any checking for overflow. The caller
           is required to make sure that the units used for the
           measurement are such that no floating point overflow will
           occur when the conversion is performed.

       2)  Some of the units are not "defined" quantities. In such a case
           a best estimate is provided as of the date of the current
           version of this routine. Those estimated quantities are:

              AU               The astronomical unit. The value was taken
                               from the JPL ephemeris DE125. This value
                               is an approximation and should not be used
                               for high-accuracy work. It agrees with the
                               value used in the JPL planetary ephemeris
                               DE430 (149597870.700 km) at the 100m
                               level.

              TROPICAL_YEARS   The tropical year is the time from equinox
                               to equinox. This varies slightly with
                               time.

              PARSECS          The parsec is the distance to an object
                               whose parallax angle is one arcsecond. Its
                               value is dependent upon the value of the
                               astronomical unit.
#### Literature_References
       None.
#### Author_and_Institution
       N.J. Bachman        (JPL)
       C.A. Curzon         (JPL)
       J. Diaz del Rio     (ODC Space)
       H.A. Neilan         (JPL)
       W.M. Owen           (JPL)
       W.L. Taber          (JPL)
       I.M. Underwood      (JPL)
#### Version
       -CSPICE Version 2.0.1, 13-AUG-2021 (JDR)

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

       -CSPICE Version 2.0.0, 13-MAY-2016 (NJB)

           Updated to support expanded names of metric distance
           units, as well as to support the abbreviation "M"
           indicating meters.

       -CSPICE Version 1.0.0, 17-MAY-1999 (NJB) (CAC) (HAN) (WMO) (WLT) (IMU)
#### Index_Entries
       convert units
#### Link to routine convrt_c source file convrt_c.c

    Fri Dec 31 18:41:03 2021