/*
 * ^NAME:  esmr_read.c 
 *
 * ^PROJECT: GSFC V0 DAAC
 *
 * ^SYNOPSIS: esmr_read < xxx.tbn > 
 *
 * ^DESCRIPTION:
 *  This software emulates the functionality of the Pascal program Rdtbnav
 *  that was submitted to the DAAC with the data files.  Its purpose is to make
 *  the binary data files generated by the ESMR instrument during the 
 *  TOGA-COARE field experiment readable on UNIX systems.
 *
 *  Background and data file structure:
 *
 *  The ESMR data files were generated on a DOS system.  Each file consists
 *  of the instrument's output during one flight.  The naming convention for
 *  these files is <julian day>.tbn.  The data is stored in 64-byte, fixed-
 *  length records each containing the following information:
 *       - Brightness temperature for each of 39 beam positions(1 scan);
 *       - A precise time code for the end of each scan
 *       - Earth location data for the aircraft
 *       - Several pieces of aircraft data:  pitch, roll, etc.
 *
 * ^ALGORITHM:
 *  The ESMR data files are formatted in 64-byte records as follows:
 *  	bytes 1-43 contain individual data values
 *	bytes 44-61 are to be read as pairs into short integers
 *	bytes 62-64 are empty
 *  Program esmr_read ingests a 64-byte record and assigns the bytes to 
 *  variables as indicated in the format documentation.  Function
 *  show_tbnav then displays the data values on the terminal screen. The file
 *  processing loop is user-driven.  The Library function fseek positions the 
 *  read pointer at the beginning of a user-requested record.
 *  
 * ^NOTES:  File ESMR.dat containing the first ten ESMR data records from 
 *  file 011.tbn are provided for validation of data output from this program. 
 *
 * ^LIMITATIONS:  A byte-swapping function (swap_short) was required to read 
 *  the data on the DAAC's SGI machines.  To help determine whether an 
 *  implementation requires a byte-swap, the bit-dumping function (bit_print) 
 *  may be enabled.
 *
 * ^AUTHOR:  Patricia L. Hrubiak 
 *
 * ^ADDRESS: Hughes STX
 *           7601 Ora Glen Dr., Suite 300 
 *           Greenbelt, MD  20770 
 * 
 * ^CREATED: 30 Dec 93 
 */ 

#ifndef __lint
static char *SccsId = "@(#)esmr_read.c 1.1      2/28/94";
#endif
 
#include <stdio.h>
#include <stdlib.h>

/*
 * Global variables  
 */

typedef struct
{
    char  bptemp[39];           /*  Brightness temps for 1 scan */
    char  hour,min,sec,secfrac; /*  time components*/
    char  other[21];            /*  2-byte data values  */
} tbnavtype;                    /*  structure declaration */


 tbnavtype  tbnav;              /*  structure variable declaration */
 FILE       *ifp, *ofp;         /*  pointers to io files */
 int        c = 0;              /*  loop control variable */
 char       byte_0,byte_1;	/*  byte buffer/swap argument */
 short      swapt;		/*  returned integer from short_swap*/
 long       isnum;              /*  variable for read pointer positioning*/

 int	    jul_day, lat, latfrac, lon, lonfrac, alt, head, roll, pitch;
	   			/*Julian day, latitude, latitude fraction,
				  longitude, longitude fraction, altitude,
				  heading, aircraft roll, aircraft pitch*/ 
 double     clat, clon, csec, calt, cpitch, croll, chead;
				/*floating point representations of latitude,
				  longitude, time, altitude, aircraft pitch,
				  aircraft roll, aircraft heading*/	
/*
 * ^FUNCTION:  bit_print
 * 
 * ^ARGUMENTS:  
 *   Type    Variable     In/Out  Description
 *   ----------------------------------------
 *   short   v            in      dumps bits in 
 *                                variable
 * ^NOTES:
 *  Function bit_print prints out a short integer in binary.  Decomment it
 *  if you need it to determine if a byte-swap is indicated.
 */
   
/*void bit_print(short v)
{
    int  i, mask = 1 << 15;  ++ mask = 100 ... 0++ 

    for (i = 1; i <= 16; ++i)
    {
        putchar(((v & mask) == 0) ? '0' : '1');
        v <<= 1;
        if (i % 8 == 0 && i != 16)
            putchar(' ');
    }
}*//* end bit-print */

/*
 * ^FUNCTION:  swap_short
 *
 * ^RETURN VALUE:  short integer y.i, a swapped pair of bytes
 *  
 * ^ARGUMENTS:
 *   Type    Variable     In/Out  Description
 *   ----------------------------------------
 *   char    p0           in      byte
 *   char    p1           in      byte
 *
 * ^NOTES:  Function swap_short is called with two 1-byte character arguments
 *  which together comprise a data value and loads them into a short integer
 *  in the reverse of the order in which they were read.  This addresses the 
 *  byte-order assignment difference between the DAAC's SGI implementation and
 *  the DOS implementation on which the ESMR files were generated.
 */

 short swap_short(char p0,char p1)
{
    union bytes
    {
        short i;
        char c[2];               
    };
    union bytes y;

    y.c[0] = p1;
    y.c[1] = p0;  

    return(y.i);
} /* end byte swap */

/*
 * ^FUNCTION:  show_tbnav
 * 
 * ^ARGUMENTS:
 *  Type      Variable    In/Out  Description
 *  -----------------------------------------
 *  structure tb_nav      in      a 64-byte (char) record 
 *
 * ^NOTES:  Function show_tbnav assigns the values ingested in structure 
 *  tbnav to specific variables and displays the record on the screen.
 *  The 45th through the 61st elements of the record are paired bytes to be
 *  read into short integers then converted to floating point variables.  The
 *  bytes are swapped then assigned to variables by a switch that uses the
 *  value of array index k to determine what an input should be from its
 *  position in array "order".
 */

void show_tbnav()
{
    int k, tbn;
    printf( "\nLeft Brightness Temps:\n");

    for (k = 0; k <= 18; k++)

    {	
      tbn = tbnav.bptemp[k]+100;
      printf("%d\t",tbn);
    }

    printf("\n\nNadir Brightness Temp:\t%d\n",(tbnav.bptemp[19]+100));

    printf("\nRight Brightness Temps:\n");

    for (k =20; k <= 38; k++)

    {
      tbn = tbnav.bptemp[k]+100;
      printf("%d\t",tbn);
    }

    for (k = 0; k <= 20; k+=2)

    {
/*	printf("\nOther[%d]=:  %d\n",k,tbnav.other[k]); */

	byte_0 = tbnav.other[k];
	byte_1 = tbnav.other[k+1];	
	swapt = swap_short(byte_0,byte_1);
/*	bit_print(swapt);*/
/*	printf("\nelement[%d] of array other =:  %d\n",k,swapt);*/

	switch (k)
{
	case 0 : jul_day = swapt;
			break;
	case 2 : lat = swapt;
			break;
	case 4 : latfrac = swapt;
		 clat = lat + .0001*latfrac;
			break;
	case 6 : lon = swapt;
			break;
	case 8 : lonfrac = swapt;
		 clon = lon + .0001*lonfrac;
			break;
	case 10 : alt = swapt;
		  calt = 10.*alt;
			break;
	case 12 : head = swapt;
		  chead = head/10.;
			break;
	case 14 : roll = swapt;
		  croll = roll/10.;
			break;
	case 16 : pitch = swapt;
		  cpitch = pitch/10.;

} /* end case */


    } /* End of display of other */

    csec = tbnav.sec + .01*tbnav.secfrac;
	
    printf("\n\nJulian Day  %d  Time:  %d:%d:%5.2f\n",
          jul_day,tbnav.hour,tbnav.min,csec);

    printf("\nLatitude:  %10.4f\tLongitude:  %10.4f\n",clat,clon);

    printf("\nAltitude:  %7.0f\tHeading:  %8.2f\n",calt,chead);

    printf("\nPitch:  %8.2f\tRoll:\t%8.2f\n",cpitch,croll);
                                      
} /* end function show_tbnav */

/*
 * ^FUNCTION:  main
 *  
 * ^ALGORITHM:  The main program is driven by a "while" loop and offers the
 *  user the options of displaying the next record in sequence, skipping to
 *  a desired record or quitting the program.  Keying in an invalid value
 *  such as characters or a negative number returns the prompt.  Keying in a
 *  number greater than the number of records in the file returns a message
 *  stating the number of records in the file followed by the prompt.
 */
    
main()
{    
  int  buf, tot, sub_tot, j, go, code;  
  long  pos;                            /*variable to hold file position*/
  char infn[8], option[10];             /*infn=filename, option=user input*/
  extern int errno, sys_nerr;           /*variable to capture system error*/
  extern char *sys_errlist[];           /*array of system error messages*/

/*
 *  Prompt user for input filename  
 */

    printf("Filename of binary TBNAV file:  ");

    scanf("%8s", infn);

/*
 *   Open input file  
 */

    if ((ifp = fopen (infn,"r")) == NULL)
      {
	if (errno >0 && errno < sys_nerr)
	{
	  fprintf(stderr," (%s)\n",sys_errlist[errno]);
	  errno = 0;
	}
	exit(0);
      }
      
/*
 *  Retrieve File Size 
 */

  fseek(ifp, 0, 2);
  pos = ftell(ifp)/64;

/*
 * Reset read pointer to beginning of file 
 */

  fseek(ifp, 0, 0);
  printf("\nFile pointer positioned at byte %d of %8s\n",ftell(ifp)/64,infn);

/*
 * Loop through input file ...     
 */

    while (c++ != EOF)  
    {

/*
 * Prompt user for request  
 */

    printf("\nPress 'n' to continue, a number to skip, or 'q' to quit: ");

    scanf("%10s", &option);

    if(option[0] == 'q')

      {
	   exit(0);
      }

    else if (option[0] == 'n')

      {
	buf = fread((char *) &tbnav, sizeof(tbnav), 1, ifp);
	printf("\nRecord %d:\n\n",ftell(ifp)/64);
	show_tbnav();
      }

    else
      {
	   sscanf(option, "%d", &isnum);

           if(isnum <= pos)
	     {
	       
	       code = fseek(ifp, ((isnum-1)*64), 0);

	       if (code == 0)
		 {
		   buf = fread((char *) &tbnav,sizeof(tbnav),1,ifp);
		   printf("\nRecord %d:\n\n",ftell(ifp)/64);
		   show_tbnav();
		 }
              } 
	    else 
	      {
		printf("\nFile %8s contains %d records. \n",infn,pos);
	      }
      } 
      
    } /* END while-not-EOF */ 

} /* END main program */