|IMAGE/VOLUME||ODD NX||EVEN NX|
Fourier files have NX changed depending on NX of the corresponding real file. For odd NX of a real file, the Fourier file will have record length NNNN=NX+1, for even NX of a real file, the Fourier file will have record length NNNN=NX+2. Thus, the record length of a Fourier file, both 2D and 3D is even.
The Fourier coefficients are written in in such a way that element (KX=0,KY=0,KZ=0) is in location (1,1,1).
First record contains Fourier coefficients:
Location in file: KX KY KZ 1,1,1 Re( 0 0 0) 2,1,1 Im( 0 0 0) 3,1,1 Re( 1 0 0) 4,1,1 Im( 1 0 0) . . NNNN-1,1,1 Re(NNNN/2 0 0) NNNN,1,1 Im(NNNN/2 0 0)
Record LY, LZ contains Fourier coefficients:
Location in file: KX KY KZ 1,LY,LZ Re( 0 LY-1 LZ-1) 2,LY,LZ Im( 0 LY-1 LZ-1) 3,LY,LZ Re( 1 LY-1 LZ-1) 4,LY,LZ Im( 1 LY-1 LZ-1) . . NNNN-1,LY,LZ Re(NNNN/2 LY-1 L-1Z) NNNN,LY,LZ Im(NNNN/2 LY-1 LZ-1)
Important: if KY>NY/2+1 the corresponding frequency becomes LY=KY-1-NY, if KZ>NZ/2+1 the corresponding frequency becomes LZ=KZ-1-NZ.