/***********************************************************

                  SUBROUTINE GEOREADTOMASK

 GEOREAD READS ALL RECORD NUMBERS OF PROFILES IN A USER 
 SPECIFIED GRID BOX.  IT DOES THIS BY FIRST GETTING INFORMATION
 ON THE SPECIFIED GRID BOX ( NUMBER OF PROFILES IN GRID BOX AND
 LOCATION OF FIRST RECORD NUMBER FOR GRID BOX IN PRIMARY MASK)
 FROM A SECONDARY MASK FILE.  USING THIS INFORMATION, THE ACTUAL
 PROFILE NUMBERS ARE READ INTO A MASK

**************************************************************/

/*************************************************************

 DEFINE IN AS A TWO INTEGER STRUCTURE.  THE FIRST INTEGER,
 IN.NUM IS THE NUMBER OF PROFILES IN A GRID BOX.  THE SECOND
 INTEGER, IN.REC, IS THE LOCATION IN THE PRIMARY FILE OF
 THE FIRST PROFILE RECORD NUMBER IN THE SPECIFIED GRID BOX.

**************************************************************/

struct write2 in;

georeadtomask_( 
 
 int *lon,             /* CHOSEN LONGITUDE */

 int *lat,             /* CHOSEN LATITUDE */

 int *numpros,         /* NUMBER OF PROFILES AT A GRID POINT */

 int *idim,            /* NUMBER OF LONGITUDE SPACINGS */

 int *fn1,             /* FILE NUMBER OF PRIMARY FILE */

 int *fn2,             /* FILE NUMBER OF SECONDARY FILE */

 int *fnout            /* OUTPUT FILE NUMBER */

          )

{

/*********************************************************

 PARAMETERS:

  SEEKNUM - POSITION OF DESIRED INFORMATION IN SECONDARY FILE.
            THIS NUMBER IS DETERMINED FROM THE INPUT LATITUDE
            MINUS ONE MULTIPLIED BY THE LONGITUDE SPACING, PLUS
            THE INPUT LONGITUDE MINUS ONE.
 IGRIDPOS - STATION POSITIONS READ IN

***********************************************************/

 int  seeknum,i,igridpos;    

/**********************************************************

 CALCULATE SECONDARY MASK POSITION

***********************************************************/

 seeknum = *idim * ( *lat - 1 ) + *lon - 1;

/**********************************************************

 MOVE FILE POINTER TO CORRECT POSITION IN SECONDARY FILE.

***********************************************************/


 fseek( fp[*fn2], seeknum * sizeof( struct write2 ), SEEK_SET );

/**********************************************************

 READ NUMBER OF PROFILES IN GRID BOX ( IN.NUM ) AND
 LOCATION OF FIRST PROFILE ( IN.REC ).

***********************************************************/

 fread( &in, sizeof( struct write2 ), 1, fp[*fn2] );

/**********************************************************

 SET NUMPROS TO THE NUMBER OF PROFILES.

***********************************************************/

 *numpros = in.num;

/***********************************************************

 USE LOCATION OF FIRST PROFILE TO MOVE FILE POINTER TO CORRECT
 POSITION IN PRIMARY FILE.

************************************************************/

 fseek( fp[*fn1], in.rec * sizeof( int ), SEEK_SET );

/***********************************************************

 READ IN PROFILE RECORD NUMBERS
 WRITE OUT TO FILE

************************************************************/

 for ( i = 1; i <= in.num; i++ ) {

  fread( &igridpos, sizeof( int ), 1, fp[*fn1] );
  fwrite( &igridpos, sizeof(int ), 1, fp[*fnout]);

 }

}