C+
C NAME:
C	SplineGridX
C PURPOSE:
C	Interpolation of 2D arrays in horizontal direction.
C CATEGORY:
C	Interpolation using natural spline
C CALLING SEQUENCE:
	subroutine SplineGridX(iFlag,XN1,XN2,XM1,XM2,NX,NY,ZN,MX,ZM)
C INPUTS:
C	iFlag		integer		1st bit set: flag bad point in output ZM if
C					    nearest grid point in input ZN is bad.
C
C					2nd bit set: if the range [XM1,XM2] extends
C					    outside [XN1,XN2] then x-coordinates outside
C					    [XN1,XN2] are mapped back inside
C					    by a mod (XN2-XN1) operation. 
C
C	XN1		real		x-coordinate of 1st  column of input  ZN
C	XN2		real		x-coordinate of last column of input  ZN
C	XM1		real		x-coordinate of 1st  column of output ZM
C	XM2		real		x-coordinate of last column of output ZM
C	NX		integer		horizontal dimensions of ZN
C	NY		integer		vertical dimensions of ZN
C	ZN(NX,NY)	real		fnc-values
C	MX		integer		new horizontal dimension
C OUTPUTS:
C	ZM(MX,NY)	real		interpolated fnc-values
C CALLS:
C	ArrR4Step, Say, SplineX
C RESTRICTIONS:
C	The in- and output user-coordinate ranges must be non-zero
C PROCEDURE:
C >	1st bit of iFlag is set: for each grid point of the output grid the
C	nearest grid point of the output grid is determined. If this nearest
C	point was flagged (contained value BadR4()) then the value of the
C	output grid is also flagged.
C	!! `Nearest' means the nearest grid point in the
C	   horizontal direction only (along a single row);
C >	For each row in ZN a spline is calculated, using all valid fnc-values
C	in that row. The ordinate for the spline is assumed to run from
C	XN1 to XN2. The spline is then used to interpolate fnc-values in
C	evenly spaced ordinate values between XM1 and XM2.
C >	If the row dimension is not changed, SplineGridX and has the effect of
C	filling in the invalid function values (if 1st bit of iFlag is set)
C MODIFICATION HISTORY:
C	JUL-1993, Paul Hick (UCSD/CASS)
C	APR-1994, Paul Hick (UCSD/CASS)
C	    added argument bFlag to control flagging of function values in the output array
C	MAY-2002, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
C	    added arguments MX and ZM to allow changes in horizontal dimension
C	    Note that the old functionality is retained by setting MX=NX, ZM=ZN
C	    Changed logical argument bFlag to integer argument iFlag. The original bFlag
C	    functionality is now controlled by the first bit in iFlag. The second bit
C	    is now used to contol the mod( XN2-XN1) ) behavior.
C-
	    integer	iFlag
	    real	XN1
	    real	XN2
	    real	XM1
	    real	XM2
	    integer	NX
	    integer	NY
	    real	ZN(NX,NY)		! Input data array
	    integer	MX
	    real	ZM(MX,NY)		! Output data array

	character	cSay*11			/'SplineGridX'/

	parameter	(NMAX = 1000)

	real		XN(NMAX)
	real		XM(NMAX)

	if (max(NX,MX) .gt. NMAX) call Say(cSay,'E','Not enough','scratch space. Increase parameter NMAX')

	call ArrR4Step(XN1,(XN2-XN1)/(NX-1),NX,XN)	! Input X-coordinates
	call ArrR4Step(XM1,(XM2-XM1)/(MX-1),MX,XM)	! Output X-coordinates

	call SplineX(iFlag,NX,XN,MX,XM,NY,ZN,ZM)

	return
	end