______________________________________________________________________________ P2 This subroutine computes a one or two-dimensional Fourier transform and/or the corresponding power spectrum of a SAD file, and writes them to a new file or files. The power spectrum is equal to the sum of the squares of the real and the imaginary parts of the (complex) Fourier transform, and may be output in a symmetric form (positive and negative frequencies) or a nonsymmetric form (only positive frequencies). The Fourier transform may be output in two different formats, either complex or in an encapsulated format where the odd columns contain the real part, and the even columns contain the imaginary part. For a file of M columns and N rows for which a two-dimensional transform is computed, the output Fourier transform will will have a size equal to (INT(M/2)+1) columns by N rows for the complex format, or 2(INT(M/2)+1) columns by N rows for the encapsulated format. The output frequencies range from 0 to 0.5 pixel pairs per pixel (0 to pi) along rows and 0 to 0.5 pixel pairs per pixel to the lowest nonzero negative frequency along columns. The power spectrum file will be INT(M/2)+1 columns by INT(N/2)+1 rows in the nonsymmetric case and 2*INT(M)/2)+1 columns by 2*INT(N/2)+1 rows in the symmetric case. ______________________________________________________________________________ Enter an option: 2-APR-1995 16:30:02.12 OPTION=P2 PWRSPEC, Version 2 Open the file whose Fourier transform and/or power spectrum is to be computed Enter the filename: (<CR> for default) FILE_IN=CE There is one map in the file Reading from the file 100 rows of 100 pixels in R4 format Enter the area to be transformed: Enter start-column end-column start-row end-row: (default = entire map) BOUNDARIES= 1 100 1 100 Enter the dimension of the fourier transform/power spectrum: (default = 2) DIMENSION= 2 Enter a command: A = Writes only the fourier transform B = Writes only the power spectrum (default) C = Writes the power spectrum and the fourier transform COMMAND=A Enter a choice for the Fourier transform format: C = Complex (default) E = Encapsulated (odd columns real; even columns imaginary FOURIER_TRANSFORM_FORMAT=E Do you wish to make the image to be transformed approximately continuous at the edges? (default = Y) CONTINUOUS= T Enter the number of pixels to be used in the cosbell smoothing on each side: (default = 4) NUMBER= 4 Enter the name of the file to contain the fourier transform: (default = TCE) FILE_FOURIER= TCE Creating new file For the Fourier transform output file Enter the ouput map number(s): (default = 1) MAPS_OUT= 1 ______________________________________________________________________________