C+
C NAME:
C	t3d_grid2_fnc
C PURPOSE:
C	Defines statement function for conversion between heliographic coordinates
C	and array index and v.v. in tomography program.
C PROCEDURE:
C	nLng, nLat, nRad and nTim are usually pulled out of the t3d array.
C
C	Each of the conversions is a linear transformation from
C	range [xb,xe] to [yb,ye].
C	For all index ranges the start value is 0.5 and the end value is
C	N+0.5, covered by N steps.
C-
	rfnc(x, xb,xe,yb,ye) = (ye*(x-xb)-yb*(x-xe))/(xe-xb)

	rCarI(A) = rfnc( A       , Cbeg,     Cend,  0.5, nLng+0.5 )
	rCarA(I) = rfnc( float(I),  0.5, nLng+0.5, Cbeg,     Cend )

	rModC(A) = Cbeg+mod(mod(A-Cbeg,Cend-Cbeg)+(Cend-Cbeg),Cend-Cbeg)

	rLngI(A) = rfnc( A       ,  0.0, 360.0   ,  0.5, nLng+0.5 )
	rLngA(I) = rfnc( float(I),  0.5, nLng+0.5,  0.0, 360.0    )

	rModL(A) = mod( mod( A, 360.0 )+360.0, 360.0 )

	rLatI(A) = rfnc( A       ,-90.0, 90.0    ,  0.5, nLat+0.5 )
	rLatA(I) = rfnc( float(I),  0.5, nLat+0.5,-90.0, 90.0     )

	rRadI(A) = rfnc( A       , Rbeg, Rend    ,  0.5, nRad+0.5 )
	rRadA(I) = rfnc( float(I),  0.5, nRad+0.5, Rbeg, Rend     )

	rTimI(A) = rfnc( A       , Tbeg, Tend    ,  0.5, nTim+0.5 )
	rTimA(I) = rfnc( float(I),  0.5, nTim+0.5, Tbeg, Tend     )