CALL SEQUENCE...
       ggdlat  GGIN GGOUT [LOLA] OUTPUT [ -a VAL1 -kind VAL2 ]
 
 
      DESCRIPTION...
       ggdlat  - LATITUDE DERIVATIVE OF A GRID SET
 
 
      AUTHOR  - J.D.Henderson, NOV 07/80.
      LAST REVISION: $Header: Corriger-l-usage-de-MAXW-et-NWDS-dans-GGDLAT-GGDLON @ 2018-06-02 16:54:22 -0400 (dugas) $
 
 
      PURPOSE - COMPUTES THE LATITUDE DERIVATIVES OF LAT-LON OR GAUSSIAN
                GRIDS IN FILE GGIN USING FINITE DIFFERENCES AND STORES
                THE RESULT ON FILE GGOUT.
 
      NOTES: 1) THE INPUT GRID TYPE IS ALWAYS ASSUMED TO BE GAUSSIAN
                WHEN DEALING WITH CCCma FILES.
             2) FOR RPN/CMC STANDARD FILES, THE SUPPORTED INPUT GRID
                TYPES ARE G (GAUSSIAN), A (LAT-LONG), B (LAT-LONG WITH
                POLES AND EQUATOR), L (GENERALIZED LAT-LONG) AND
                ROTATED, Z (VARIABLE-RESOLUTION LAT-LONG). NOTE
                THAT U GRIDS (YinYan) ARE **NOT** SUPPORTED.
 
      NOTES CONCERNING THE USE OF FILE LOLA...
             1) THE COORDINATES IN LOLA WILL GENERALLY REFER TO A
                NON-ROTATED STANDARD GEOGRAPHICAL FRAME OF REFERENCE.
             2) THE FILE SHOULD HOLD 2D 'LO' AND 'LA' VARIABLES, BOTH
                IN UNITS OF DEGREES.
             3) THIS FILE CAN ONLY BE USED WITH 'Z' GRID TYPES. IF IT
                IS NOT PROVIDED, OPERATIONS ON A 'Z' GRID WILL BE DONE
                IN THE GRID'S OWN FRAME OF REFERENCE.
 
 
      INPUT FILE...
       GGIN  = GLOBAL OR HEMISPHERIC GRIDS
       LOLA  = [OPTIONAL] 2D GRID POINT LONGITUDES AND LATITUDES.
 
 
      OUTPUT FILE...
       GGOUT = LATITUDE DERIVATIVES.
 
 
      INPUT PARAMETERS (ONLY USED WHEN FILE LOLA IS SPECIFIED)...
 
       A     = DELTA LATITUDE VALUE TO BE USED IN DERIVATIVE (IN DEGREES).
               THE FORWARD AND BACKWARD FINITE DIFFERENCE POINTS WILL BE
               INTERPOLATED FROM THEIR (LON,LAT) POSITION TO (LON,LAT+A)
               AND (LON,LAT-A) POSITIONS.
       KIND >= 0; INTERPOLATION TYPE
               1 FOR LINEAR,
               2 FOR NEAREST NEIGHBOR (only RPN/CMC Standard files)
                 OTHERWISE CUBIC
            <  0 INTERPOLATION IS LINEAR
 
      
 
      EXIT CONDITIONS...
        0 NO PROBLEMS
        1 ABORT ERROR READING GGIN
        2 UNSUPPORTED GRID TYPE
        3 ABORT ERROR READING LOLA
        4 LOLA AND GGIN ARRAYS DIFFER IN SIZE
        5 UNABLE TO READ LONGITUDE FROM LOLA
        6 UNABLE TO READ LATITUDE FROM LOLA
        7 ERROR READING A AND/OR KIND PARAMS