GRASS GIS 7 Programmer's Manual  7.5.svn(2017)-r71817
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getg.c
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1 /* Name: getg.c
2  *
3  * Created: Thu May 29 00:37:44 1986
4  * Last modified: Sat May 31 20:34:30 1986
5  *
6  * Purpose: Get the laplacian of a Gaussian (not normalized).
7  *
8  * Author: Bill Hoff,2-114C,8645,3563478 (hoff) at uicsl
9  */
10 
11 #include <stdio.h>
12 #include <math.h>
13 #include <grass/gmath.h>
14 
15 
16 int getg(double w, double *g[2], int size)
17 {
18  long i, j, totsize, n, g_row;
19  float rsq, sigma, two_ssq, val, sum = 0.0;
20 
21  totsize = size * size;
22  n = size / 2;
23  for (i = 0; i < totsize; i++) {
24  *(g[0] + i) = 0.0;
25  *(g[1] + i) = 0.0;
26  }
27 
28  sigma = w / (2.0 * sqrt((double)2.0));
29  two_ssq = 2.0 * sigma * sigma;
30  for (i = 0; i < n; i++) {
31  g_row = i * size; /* start of row */
32  for (j = 0; j < n; j++) {
33  rsq = i * i + j * j;
34  val = (rsq / two_ssq - 1) * exp(-rsq / two_ssq);
35  *(g[0] + g_row + j) = val;
36  sum += val;
37  /* reflect into other quadrants */
38  if (j > 0) {
39  *(g[0] + g_row + (size - j)) = val;
40  sum += val;
41  }
42  if (i > 0) {
43  *(g[0] + (size - i) * size + j) = val;
44  sum += val;
45  }
46  if (i > 0 && j > 0) {
47  *(g[0] + (size - i) * size + (size - j)) = val;
48  sum += val;
49  }
50  }
51  }
52 
53  *(g[0] + 0) -= sum; /* make sure sum of all values is zero */
54 
55  return 0;
56 }
int getg(double w, double *g[2], int size)
Definition: getg.c:16
float g
Definition: named_colr.c:8