Source coordinate system: imaginary 3D seismic acquisition bin grid.  The two axes are orthogonal, but the unit on the I-axis is 25 metres, whilst the unit on the J-axis is 12.5 metres.¶The target projected coordinate system is WGS 84 / UTM Zone 31N and the origin of the bin grid (centre of bin 0,0) is defined at E = 456781.0, N = 5836723.0.  The projected coordinate system point scale factor at the bin grid origin is 0.99984.¶The map grid bearing of the I and J axes are 110* and 20* respectively.  Thus the angle through which both the positive I and J axes need to be rotated to coincide with the positive Easting axis and Northing axis respectively is +20 degrees.¶¶Hence: ¶XT0 ,	=    456 781.0 m¶YT0	= 5 836 723.0 m¶dSX 	= 25¶dSY	= 12.5¶k 	= 0.99984¶q	= +20 degrees¶¶Forward calculation for centre of bin with coordinates: I = 300, J = 247:¶¶XT = Easting   = XT0   +   XS . k . dSX . cos q   +   YS . k . dSY  . sin q    = 464 855.62 m.¶¶YT = Northing = YT0   –   XS . k . dSX . sin q    +   YS . k . dSY  . cos q  = 5 837 055.90 m¶¶Reverse calculation for this point:¶XS = [( XT  – XT0) . cos qY  –  (YT – YT0) . sin qY ] / [k . dSX  . cos (qX – qY)] = 230 bins¶¶YS = [(XT   – XT0) . sin qX   +  (YT – YT0) . cos qX ] / [k . dSY . cos (qX – qY)]  = 162 bins