/// <summary>
/// Clusters the specified items.
/// </summary>
/// <param name="itemsToBeClustered">The items to be clustered.</param>
/// <returns>The set of clustered map items.</returns>
public static IEnumerable<MapItem> Cluster(IEnumerable<MapItem> itemsToBeClustered)
{
// Add all of the items to a map item quad tree.
MapItemQuadTree tree = new MapItemQuadTree();
foreach (MapItem item in itemsToBeClustered)
{
tree.Add(item);
}
Dictionary<int, List<MapItemQuadTreeNode>> nodesByZoomLevel = GroupNodesByZoomLevel(tree);
// Sort all of the zoom levels present in descending order.
List<int> zoomLevels = new List<int>(nodesByZoomLevel.Keys);
zoomLevels.Sort();
zoomLevels.Reverse();
// Iterate over all zoom levels from finest to coarsest...
foreach (int zoomLevel in zoomLevels)
{
// ...and cluster each node, one by one.
foreach (var node in nodesByZoomLevel[zoomLevel])
{
ClusterNodeItems(tree, node);
}
}
// A single map item may appear in multiple nodes, so take care not to return duplicates.
HashSet<MapItem> items = new HashSet<MapItem>();
foreach (var node in tree.Nodes)
{
foreach (var item in node.Items)
{
items.Add(item);
}
}
return items;
}
/// <summary>
/// Clusters the map items contained in the node. Clustered items are modified and new items are added
/// to the tree to represent the clusters.
/// </summary>
private static void ClusterNodeItems(MapItemQuadTree tree, MapItemQuadTreeNode node)
{
var clumps = new List<List<MapItem>>();
var clusters = new List<Tuple<List<MapItem>, Point>>();
HashSet<MapItem> visitedNodes = new HashSet<MapItem>();
// Create the set of clusters of intersecting items.
foreach (var item in node.Items)
{
List<MapItem> clump = new List<MapItem>();
GrowClump(tree, item, node.ZoomLevel, visitedNodes, clump);
if (clump.Count > 1)
{
foreach (var cluster in ClusterClump(clump, node.ZoomLevel))
{
if (cluster.Item1.Count > 1)
{
clusters.Add(cluster);
}
}
}
}
// For each cluster, modify the existing items in the cluster such that they don't appear at the same
// LOD as the cluster and add new item(s) to the tree that represent the cluster.
foreach (var cluster in clusters)
{
Debug.Assert(cluster.Item1.Count > 1);
Point clusterLocation = cluster.Item2;
var clusterItem = new FixedSizeInScreenSpaceMapItem(
clusterLocation.ToLocation(),
PositionOrigin.Center,
new Size(20, 20),
0,
node.ZoomLevel);
tree.Add(clusterItem);
foreach (var item in cluster.Item1)
{
tree.Remove(item);
// If this item isn't present at a finer LOD than this, then it's been totally
// subsumed by the cluster; otherwise, re-add it to the tree with adjusted
// min zoom level.
if (item.MaxZoomLevel > node.ZoomLevel)
{
var adjustedItem = new FixedSizeInScreenSpaceMapItem(
item.Location,
PositionOrigin.Center,
new Size(20, 20),
node.ZoomLevel + 1,
item.MaxZoomLevel)
{
Parent = clusterItem
};
// We're removing the item, so re-assign the children's parent to the cluster that's
// standing in for it.
foreach (var child in item.Children)
{
child.Parent = adjustedItem;
adjustedItem.AddChild(child);
}
clusterItem.AddChild(adjustedItem);
tree.Add(adjustedItem);
}
}
}
}