fft.c

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/**
 * \file fft.c
 *
 * \brief Fast Fourier Transformation of Two Dimensional Satellite Data functions.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or (at
 * your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * \author GRASS GIS Development Team
 *
 * \date 2001-2006
 */

#include <grass/config.h>

#if defined(HAVE_FFTW_H) || defined(HAVE_DFFTW_H) || defined(HAVE_FFTW3_H)

#ifdef HAVE_FFTW_H
#include <fftw.h>
#endif

#ifdef HAVE_DFFTW_H
#include <dfftw.h>
#endif

#ifdef HAVE_FFTW3_H
#include <fftw3.h>
#define c_re(c) ((c)[0])
#define c_im(c) ((c)[1])
#endif

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <grass/gmath.h>
#include <grass/gis.h>


/**
 * \fn int fft2(int i_sign, double (*data)[2], int NN, int dimc, int dimr)
 *
 * \brief Fast Fourier Transform for two-dimensional array.
 *
 * Fast Fourier Transform for two-dimensional array.<br>
 * <bNote:</b> If passing real data to fft() forward transform 
 * (especially when using fft() in a loop), explicitly (re-)initialize 
 * the imaginary part to zero (DATA[1][i] = 0.0). Returns 0.
 *
 * \param[in] i_sign Direction of transform -1 is normal, +1 is inverse
 * \param[in,out] data Pointer to complex linear array in row major order 
 * containing data and result
 * \param[in] NN Value of DATA dimension (dimc * dimr)
 * \param[in] dimc Value of image column dimension (max power of 2)
 * \param[in] dimr Value of image row dimension (max power of 2)
 * \return int always returns 0
 */

int fft2(int i_sign, double (*data)[2], int NN, int dimc, int dimr)
{
#ifdef HAVE_FFTW3_H
    fftw_plan plan;
#else
    fftwnd_plan plan;
#endif
    double norm;
    int i;

    norm = 1.0 / sqrt(NN);

#ifdef HAVE_FFTW3_H
    plan = fftw_plan_dft_2d(dimr, dimc, data, data,
                            (i_sign < 0) ? FFTW_FORWARD : FFTW_BACKWARD,
                            FFTW_ESTIMATE);

    fftw_execute(plan);

    fftw_destroy_plan(plan);
#else
    plan = fftw2d_create_plan(dimc, dimr,
                              (i_sign < 0) ? FFTW_FORWARD : FFTW_BACKWARD,
                              FFTW_ESTIMATE | FFTW_IN_PLACE);

    fftwnd_one(plan, data, data);

    fftwnd_destroy_plan(plan);
#endif

    for (i = 0; i < NN; i++) {
        data[i][0] *= norm;
        data[i][1] *= norm;
    }

    return 0;
}

/**
 * \fn int fft(int i_sign, double *DATA[2], int NN, int dimc, int dimr)
 *
 * \brief Fast Fourier Transform for two-dimensional array.
 *
 * Fast Fourier Transform for two-dimensional array.<br>
 * <bNote:</b> If passing real data to fft() forward transform 
 * (especially when using fft() in a loop), explicitly (re-)initialize 
 * the imaginary part to zero (DATA[1][i] = 0.0). Returns 0.
 *
 * \param[in] i_sign Direction of transform -1 is normal, +1 is inverse
 * \param[in,out] DATA Pointer to complex linear array in row major order 
 * containing data and result
 * \param[in] NN Value of DATA dimension (dimc * dimr)
 * \param[in] dimc Value of image column dimension (max power of 2)
 * \param[in] dimr Value of image row dimension (max power of 2)
 * \return int always returns 0
 */

int fft(int i_sign, double *DATA[2], int NN, int dimc, int dimr)
{
    fftw_complex *data;
    int i;

    data = (fftw_complex *) G_malloc(NN * sizeof(fftw_complex));

    for (i = 0; i < NN; i++) {
        c_re(data[i]) = DATA[0][i];
        c_im(data[i]) = DATA[1][i];
    }

    fft2(i_sign, data, NN, dimc, dimr);

    for (i = 0; i < NN; i++) {
        DATA[0][i] = c_re(data[i]);
        DATA[1][i] = c_im(data[i]);
    }

    G_free(data);

    return 0;
}

#endif /* HAVE_FFT */