C+
C NAME:
C	t3d_grid_fnc
C PURPOSE:
C	Defines statement function for conversion between heliographic coordinates
C	and array index and v.v. in tomography program.
C RESTRICTIONS:
C	Contains statement functions, so must be called at the end
C	of the declaration section.
C PROCEDURE:
C	Statement functions for converting between modified Carrington variables and latitudes
C	(deg) and array indices.
C	nLng, nLat will usually be provided as arguments to the subroutine using this include file.
C	Note that the following variable must be defined before the functions are called
C		nLng1=nLng-1
C		nLat1=nLat-1
C		XCrange=XCend-XCbeg
C
C	XCindx	:	X=XCbeg -> I=nLng	X=XCend -> I=1
C	XCvar	:	I=nLng	-> X=XCbeg	I=1	-> X=XCend
C
C	XCmod	:	maps any XC value into the range [XCbeg,XCend] by a mod(XCrange) operation
C
C	XLindx	:	X=-90	-> J=1		X=90	-> J=nLat
C	XLdeg	:	J=1	-> X=-90	J=nLat	-> X=90
C-
	XCindx(X) = nLng-(X-XCbeg)/XCrange*nLng1
	XCvar (I) = XCbeg+1.*(nLng-I)/nLng1*XCrange	! Integer input
	!XCvarX(X) = XCbeg+   (nLng-X)/nLng1*XCrange	! Real input (used in ExtractMap only)

	XCmod (X) = XCbeg+mod(mod(X-XCbeg,XCrange)+XCrange,XCrange)

	XLindx(X) = 1+((X+90.)/180.)*nLat1		! Latitude (deg)   -> index in [1,nLat]
	XLdeg (J) = 90.*(-1.+2.*(J-1)/nLat1)		! Index in [1,nLat]-> latitude (deg)

	RRindx(R) =  1+(R-RR)/dRR
	RRhght(I) = RR+(I- 1)*dRR

	TTindx(T) =  1+(T-TT)*dTTi
	TTtime(I) = TT+(I- 1)*dTT