GRDHDR

     GRDHDR is a list of the valid grid header flags, separated by
     slashes.

	Horizontal Remap Type / Directional Grid Type

     The values in GRDHDR are set in the header array of the grid
     stored in a GEMPAK data file. The values for horizontal remap
     type define how the grid is to be interpolated to a new 
     navigation. The directional grid type flag identifies grids
     that are direction grids and therefore must be handled differently
     when interpolated from one navigation to another.

     The Horizontal Remap Type has values 0, 1 or 2 defined as the 
     following:

	0 = Regular area averaging for continuous gribs
	1 = Discrete field, use nearest neighbor
	2 = Force bilinear interpolation

     The Directional Grid Type has values 0, 1, or 2 defined as the
     following:

	0 = NOT a directional field
	1 = IS a directional field in degrees
	2 = IS a directional field in radians 

     If any flag is not given by the user, the value is set to a
     default of 0.

     The setting of the grid header elements is done automatically
     by programs like NAGRIB and the objective analysis programs.
     GDMOD may be used to change the setting of the grid header
     elements.  The header elements are all zero for grids created 
     prior to the introduction of the remapping capability.