hough_transform.c

#include <stdio.h>

int main()
{
  int points[10][2], table[20][100];
  int nPoints, cal_a, cal_b, max;

  printf("Enter number of points: ");
  scanf("%d", &nPoints);

  for (int i = 0; i < nPoints; i++)
  {
    printf("Enter points leaving space between x and y:\n");
    scanf("%d%d", &points[i][0], &points[i][1]);
  }

  for (int i = 0; i < 20; i++)
  {
    for (int j = 0; j < 100; j++)
    {
      table[i][j] = 0;
    }
  }

  for (int j = 0; j < nPoints; j++)
  {
    for (int i = -9; i < 10; i++)
    {

      cal_a = i;
      cal_b = points[j][1] - points[j][0] * i;

      // Make sure index is positive
      table[cal_a + 9][cal_b + 50] += 1;
    }
  }

  for (int i = 0; i < 20; i++)
  {
    for (int j = 0; j < 100; j++)
    {
      if (max < table[i][j])
      {
        max = table[i][j];
        cal_a = i - 9;
        cal_b = j - 50;
      }
    }
  }

  printf("There are %d collinear points\n", max);
  printf("They are: ");
  for (int i = 0; i < nPoints; i++)
  {
    if ((points[i][1] - points[i][0] * cal_a) == cal_b)
    {
      printf("(%d, %d) ", points[i][0], points[i][1]);
    }
  }
  printf("\n");
  return 0;
}

/* OUTPUT:
Enter number of points: 4
Enter points leaving space between x and y:
1 1
Enter points leaving space between x and y:
2 3
Enter points leaving space between x and y:
3 3
Enter points leaving space between x and y:
4 4
There are 3 collinear points
They are: (1, 1) (3, 3) (4, 4)

*/