public static List<List<int>> GetGroups(List<int>edges,
int img_width, int img_height,
int image_border,
int minimum_size_percent,
bool squares_only,
int max_search_depth,
bool ignore_periphery,
int grouping_radius_percent)
{
#if SHOW_TIMINGS
stopwatch timer_grouping = new stopwatch();
timer_grouping.Start();
#endif
const int compression = 4;
int grouping_radius = grouping_radius_percent * img_width / (100 * compression);
List<List<int>> groups = new List<List<int>>();
// find line segments of significant length
List<float> centres = null;
List<float> bounding_boxes = null;
List<List<int>> line_segments =
DetectLongestPerimeters(edges,
img_width, img_height,
image_border,
minimum_size_percent,
squares_only,
max_search_depth,
ignore_periphery,
ref centres,
ref bounding_boxes);
bool[][] grouping_matrix = new bool[line_segments.Count][];
for (int i = 0; i < line_segments.Count; i++)
grouping_matrix[i] = new bool[line_segments.Count];
// map out the line segments
const int step_size = 4;
int ty = img_height-1;
int by = 0;
int tx = img_width-1;
int bx = 0;
int[,] line_segment_map = new int[(img_width/compression)+2, (img_height/compression)+2];
for (int i = 0; i < line_segments.Count; i++)
{
List<int> line_segment = line_segments[i];
for (int j = 0; j < line_segment.Count; j += step_size)
{
int x = line_segment[j]/compression;
int y = line_segment[j+1]/compression;
if (line_segment_map[x, y] > 0)
{
if (line_segment_map[x, y] != i + 1)
{
int segment_index1 = line_segment_map[x, y]-1;
int segment_index2 = i;
// link the two segments
grouping_matrix[segment_index1][segment_index2] = true;
grouping_matrix[segment_index2][segment_index1] = true;
}
}
line_segment_map[x, y] = i + 1;
if (x < tx) tx = x;
if (x > bx) bx = x;
if (y < ty) ty = y;
if (y > by) by = y;
}
}
// horizontal grouping
for (int y = ty; y <= by; y++)
{
int prev_segment_index = -1;
int prev_segment_x = -1;
for (int x = tx; x <= bx; x++)
{
int segment_index = line_segment_map[x, y];
if (segment_index > 0)
{
if (prev_segment_x > -1)
{
int dx = x - prev_segment_x;
if (dx < grouping_radius)
{
if (!grouping_matrix[segment_index-1][prev_segment_index])
{
// get the line segment indexes
segment_index--;
if (segment_index != prev_segment_index)
{
// link the two segments
grouping_matrix[segment_index][prev_segment_index] = true;
grouping_matrix[prev_segment_index][segment_index] = true;
}
}
}
}
prev_segment_x = x;
prev_segment_index = line_segment_map[x, y]-1;
}
}
}
// horizontal grouping
for (int x = tx; x <= bx; x++)
{
int prev_segment_y = -1;
int prev_segment_index = -1;
for (int y = ty; y <= by; y++)
{
int segment_index = line_segment_map[x, y];
if (segment_index > 0)
{
if (prev_segment_y > -1)
{
int dy = y - prev_segment_y;
if (dy < grouping_radius)
{
if (!grouping_matrix[segment_index-1][prev_segment_index])
{
// get the line segment indexes
segment_index--;
if (segment_index != prev_segment_index)
{
// link the two segments
grouping_matrix[segment_index][prev_segment_index] = true;
grouping_matrix[prev_segment_index][segment_index] = true;
}
}
}
}
prev_segment_y = y;
prev_segment_index = line_segment_map[x, y]-1;
}
}
}
// turn grouping matrix into a hypergraph
hypergraph graph = new hypergraph(grouping_matrix.Length, 1);
for (int i = 0; i < grouping_matrix.Length; i++)
{
for (int j = 0; j < grouping_matrix[i].Length; j++)
{
if (grouping_matrix[i][j])
graph.LinkByIndex(j, i);
}
}
// detect connected sets within the hypergraph
for (int i = 0; i < graph.Nodes.Count; i++)
{
bool already_grouped = graph.GetFlagByIndex(i, 0);
if (!already_grouped)
{
List<hypergraph_node> connected_set = new List<hypergraph_node>();
graph.PropogateFlagFromIndex(i, 0, connected_set);
List<hypergraph_node> members = new List<hypergraph_node>();
for (int j = 0; j < connected_set.Count; j++)
{
if (!members.Contains(connected_set[j])) members.Add(connected_set[j]);
}
List<int> group_members = new List<int>();
for (int j = 0; j < members.Count; j++)
{
int line_segment_index = members[j].ID;
List<int> perim = line_segments[line_segment_index];
for (int k = 0; k < perim.Count; k++)
group_members.Add(perim[k]);
}
groups.Add(group_members);
}
}
#if SHOW_TIMINGS
timer_grouping.Stop();
//if (timer_grouping.time_elapsed_mS > 20)
Console.WriteLine("GetGroups: " + timer_grouping.time_elapsed_mS.ToString() );
#endif
return(groups);
}
