GEO_get_sample_time.c

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/* file: GEO_get_sample_time.c */
 
#include "GEO_geo.h"
#include "GEO_global_arrays.h"
#include "GEO_inst.h"
#include "GEO_parameters.h"
#include "GEO_output.h"
#include "PGS_MODIS_35251.h"
 
PGSt_double GEO_get_sample_time( 
        focal_plane_geometry_struct const *geometry_params,
    const int sample_number
    )
{
/*
!C*****************************************************************************
!Description:   subroutine in Instrument Model of the Level-1A geolocation 
                software to calculate the sample time offset of a pixel from
        the sector start time.  It incorporates the time offset from
        the first band collected (Band 30) to the selected band and 
        also corrects for the latch-up time (trailing edge) to the 
        sample center time.  The equations are derived in the 
        Geolocation ATBD (pp. 32-33).  
 
!Input Parameters: 
                geometry_params - Numbers describing the MODIS instrument
        sample_number - the sample number 
        
!Output Parameters:
                None
 
Return values:
            The sample time offset in seconds from the EV sector start time.    
 
Externally Defined:
                FIRST_BAND              "GEO_geo.h"
                GEO_DOUBLE_FILLVALUE    "GEO_output.h"
                LATCH_TO_CENTER         "GEO_geo.h"
                MODIS_E_BAD_INPUT_ARG   "PGS_MODIS_35251.h"
 
Call functions: None
 
Called by:      GEO_locate_one_scan     "GEO_output.h"
 
!Revision History:
        $Log: GEO_get_sample_time.c,v $
        Revision 6.2  2009/05/15 16:42:35  xgeng
        Corrected the formula to calculate the sample time
 
                Xu Geng (xu.geng@saic.com)
        Revision 6.1  2009/05/06 19:10:18  xgeng
        Changed all global variables into pointer parameters.
        Considered sample time for high resolution bands.
            
        Revision 2.2  1999/02/08 22:31:12  kuyper
        Corrected to reflect fact that EV start time corresponds to the start of
          integration for band 30, not the end.
 
 * Revision 2.1  1997/10/21  18:16:22  kuyper
 * Returned from ClearCase
 *
 * Revision 1.5.1.1  1997/07/21  22:20:17  kuyper
 * Merged in out-of-sequence changes.
 *
 * Revision 1.5  1997/07/21  16:24:34  kuyper
 * Baselined Version 1
 *
 *Parallel development:
 * Revision 1.6  1997/04/21  22:33:23  fhliang
 * commented unused argument (LL.12-14).
 *
 * Revision 1.5  1997/03/26  18:06:20  fhliang
 * Initial revision of SDST delivery of GEO_get_sample_time.c.
 *
        Revision 1.4  1996/07/24 21:02:24  kuyper
        Declared arguments const.
 
        Revision 1.3  1996/07/23 23:06:58  kuyper
        Inserted required '!' in comments.
        Changed constants to double to avoid conversions.
        Made implicit casts explicit.
 
        Revision 1.2  1996/07/18 16:40:53  kuyper
        Included self-checking header file.
        Replaced extern declaration of sample_time with definition.
        Replaced other extern declarations with corresponding header files.
 
 
        4/25/95
        Ruiming Chen
        Finished coding.
 
        6/12/95
        Frederick S. Patt (patt@modis-xl.gsfc.nasa.gov)
        Revised to change hardcoded values to defined constants 
        and improve documentation.
 
        6/22/95
        Frederick S. Patt (patt@modis-xl.gsfc.nasa.gov)
        Added band_number as global variable.
 
!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 t_sample = 1.0/3000.0; 
  char filefunc[] = __FILE__ ", GEO_get_sample_time"; 
 
  if (geometry_params == NULL) { 
    modsmf(MODIS_E_BAD_INPUT_ARG, "geometry_params is null", filefunc);
    return GEO_DOUBLE_FILLVALUE;
  }
 
  /* calculate the sample time */
  t_sample = geometry_params->t_frame / 
     (double)geometry_params->N_samp[geometry_params->band_number];
 
  return t_sample*(double)(sample_number + 1 -  
         geometry_params->N_samp[geometry_params->band_number]) +  
         geometry_params->t_frame*(
               geometry_params->band_position[geometry_params->band_number] - 
               geometry_params->F_offset[geometry_params->band_number] -  
           geometry_params->band_position[FIRST_BAND]) + 
         LATCH_TO_CENTER*(t_sample + geometry_params->t_reset);
 
}