GEO_vec_unit3.c

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/* file: GEO_vec_unit3.c */
 
#include <float.h>
#include "PGS_MODIS_35251.h"
#include "smfio.h"
#include "GEO_basic.h"
#include "GEO_util.h"
 
int  GEO_vec_unit3(
    double vec[3],
    double unit_vec[3]
        )
/*
!C*****************************************************************************
!Description:   subroutine in the utility functions of the Level-1A geolocation
                software to calculate the unit vector of a 3 element vector.
 
!Input Parameters:
        double vec[3] - the input 3-vector 
 
!Output Parameters:
            double unit_vec[3] - the unit vector from the input 3-vector
 
Call functions: modsmf(MODIS_X_MNEMONIC_STRING, "user message string", "function,
                GEO_vec_unit3.c") - writes error status messages to log
 
!Revision History:
        $Log: GEO_vec_unit3.c,v $
        Revision 1.6  1997/07/21 16:24:34  kuyper
        Baselined Version 1
 
 * Revision 1.6  1997/03/26  18:17:18  fhliang
 * Initial revision of SDST delivery of GEO_vec_unit3.c.
 *
        Revision 1.5  1997/03/10 17:30:41  kuyper
        Changed to inequality test on vec_length.
 
        Revision 1.4  1997/02/13 19:59:52  kuyper
        Merged seed files
        Added RCS Log keyword.
 
        James Kuyper Jr. (kuyper@ltpmail.gsfc.nasa.gov)
 
        6/30/95
        Tracey W. Holmes (holmes@modis-xl.gfsc.nasa.gov)
        Added SDP error messages.
 
        6/12/95
        Frederick S. Patt (patt@modis-xl.gsfc.nasa.gov)
        Revised prolog.
 
        4/5/95
        Ruiming Chen (rchen@ltpmail.gsfc.nasa.gov)
        Finished coding.
 
!Team-unique Header:
                This software is developed by the MODIS Science Data Support
                Team for the National Aeronautics and Space Administration,
                Goddard Space Flight Center, under contract NAS5-32373.
 
!END*************************************************************************
*/
{
  double vec_length = 0.0;  /* vector length */
  int i = 0;  /* iteration parameter */
 
  GEO_vec_length3(vec, &vec_length);
  if (vec_length < DBL_MIN) {
    /* write to SDP event message */
    modsmf(MODIS_E_UTIL_VEC, "", "GEO_vec_unit3, GEO_vec_unit3"); 
 
    return FAIL;
  }
 
  for (i = 0; i < 3; ++i)
    unit_vec[i] = vec[i] / vec_length;
 
  return SUCCESS;
}