GRASS GIS 8 Programmer's Manual 8.3.2(2024)-exported
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fft.c
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1/**
2 * \file fft.c
3 *
4 * \brief Fast Fourier Transformation of Two Dimensional Satellite Data
5 * functions.
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 2 of the License, or (at
10 * your option) any later version.
11 *
12 * This program is distributed in the hope that it will be useful, but
13 * WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 *
21 * \author GRASS GIS Development Team
22 *
23 * \date 2001-2006
24 */
25
26#include <grass/config.h>
27
28#if defined(HAVE_FFTW_H) || defined(HAVE_DFFTW_H) || defined(HAVE_FFTW3_H)
29
30#ifdef HAVE_FFTW_H
31#include <fftw.h>
32#endif
33
34#ifdef HAVE_DFFTW_H
35#include <dfftw.h>
36#endif
37
38#ifdef HAVE_FFTW3_H
39#include <fftw3.h>
40#define c_re(c) ((c)[0])
41#define c_im(c) ((c)[1])
42#endif
43
44#include <stdlib.h>
45#include <stdio.h>
46#include <math.h>
47#include <grass/gmath.h>
48#include <grass/gis.h>
49
50/**
51 * \fn int fft2(int i_sign, double (*data)[2], int NN, int dimc, int dimr)
52 *
53 * \brief Fast Fourier Transform for two-dimensional array.
54 *
55 * Fast Fourier Transform for two-dimensional array.<br>
56 * <bNote:</b> If passing real data to fft() forward transform
57 * (especially when using fft() in a loop), explicitly (re-)initialize
58 * the imaginary part to zero (DATA[1][i] = 0.0). Returns 0.
59 *
60 * \param[in] i_sign Direction of transform -1 is normal, +1 is inverse
61 * \param[in,out] data Pointer to complex linear array in row major order
62 * containing data and result
63 * \param[in] NN Value of DATA dimension (dimc * dimr)
64 * \param[in] dimc Value of image column dimension (max power of 2)
65 * \param[in] dimr Value of image row dimension (max power of 2)
66 * \return int always returns 0
67 */
68
69int fft2(int i_sign, double (*data)[2], int NN, int dimc, int dimr)
70{
71#ifdef HAVE_FFTW3_H
72 fftw_plan plan;
73#else
74 fftwnd_plan plan;
75#endif
76 double norm;
77 int i;
78
79 norm = 1.0 / sqrt(NN);
80
81#ifdef HAVE_FFTW3_H
82 plan = fftw_plan_dft_2d(dimr, dimc, data, data,
83 (i_sign < 0) ? FFTW_FORWARD : FFTW_BACKWARD,
84 FFTW_ESTIMATE);
85
86 fftw_execute(plan);
87
88 fftw_destroy_plan(plan);
89#else
90 plan = fftw2d_create_plan(dimc, dimr,
91 (i_sign < 0) ? FFTW_FORWARD : FFTW_BACKWARD,
92 FFTW_ESTIMATE | FFTW_IN_PLACE);
93
94 fftwnd_one(plan, data, data);
95
96 fftwnd_destroy_plan(plan);
97#endif
98
99 for (i = 0; i < NN; i++) {
100 data[i][0] *= norm;
101 data[i][1] *= norm;
102 }
103
104 return 0;
105}
106
107/**
108 * \fn int fft(int i_sign, double *DATA[2], int NN, int dimc, int dimr)
109 *
110 * \brief Fast Fourier Transform for two-dimensional array.
111 *
112 * Fast Fourier Transform for two-dimensional array.<br>
113 * <bNote:</b> If passing real data to fft() forward transform
114 * (especially when using fft() in a loop), explicitly (re-)initialize
115 * the imaginary part to zero (DATA[1][i] = 0.0). Returns 0.
116 *
117 * \param[in] i_sign Direction of transform -1 is normal, +1 is inverse
118 * \param[in,out] DATA Pointer to complex linear array in row major order
119 * containing data and result
120 * \param[in] NN Value of DATA dimension (dimc * dimr)
121 * \param[in] dimc Value of image column dimension (max power of 2)
122 * \param[in] dimr Value of image row dimension (max power of 2)
123 * \return int always returns 0
124 */
125
126int fft(int i_sign, double *DATA[2], int NN, int dimc, int dimr)
127{
128 fftw_complex *data;
129 int i;
130
131 data = (fftw_complex *)G_malloc(NN * sizeof(fftw_complex));
132
133 for (i = 0; i < NN; i++) {
134 c_re(data[i]) = DATA[0][i];
135 c_im(data[i]) = DATA[1][i];
136 }
137
138 fft2(i_sign, data, NN, dimc, dimr);
139
140 for (i = 0; i < NN; i++) {
141 DATA[0][i] = c_re(data[i]);
142 DATA[1][i] = c_im(data[i]);
143 }
144
145 G_free(data);
146
147 return 0;
148}
149
150#endif /* HAVE_FFT */
void G_free(void *buf)
Free allocated memory.
Definition alloc.c:150