private void LoadSpatialIndex(bool forceRebuild, bool loadFromFile)
{
//Only load the tree if we haven't already loaded it, or if we want to force a rebuild
if (_tree == null || forceRebuild)
{
// Is this a web application? If so lets store the index in the cache so we don't
// need to rebuild it for each request
if (HttpContext.Current != null)
{
//Check if the tree exists in the cache
if (HttpContext.Current.Cache[_filename] != null)
_tree = (QuadTree)HttpContext.Current.Cache[_filename];
else
{
_tree = !loadFromFile ? CreateSpatialIndex() : CreateSpatialIndexFromFile(_filename);
//Store the tree in the web cache
//TODO: Remove this when connection pooling is implemented
HttpContext.Current.Cache.Insert(_filename, _tree, null, Cache.NoAbsoluteExpiration,
TimeSpan.FromDays(1));
}
}
else if (!loadFromFile)
_tree = CreateSpatialIndex();
else
_tree = CreateSpatialIndexFromFile(_filename);
}
}
/// <summary>
/// Forces a rebuild of the spatial index. If the instance of the ShapeFile provider
/// uses a file-based index the file is rewritten to disk.
/// </summary>
public void RebuildSpatialIndex()
{
if (_fileBasedIndex)
{
if (File.Exists(_filename + ".sidx"))
File.Delete(_filename + ".sidx");
_tree = CreateSpatialIndexFromFile(_filename);
}
else
_tree = CreateSpatialIndex();
if (HttpContext.Current != null)
//TODO: Remove this when connection pooling is implemented:
HttpContext.Current.Cache.Insert(_filename, _tree, null, Cache.NoAbsoluteExpiration, TimeSpan.FromDays(1));
}
private void Dispose(bool disposing)
{
if (!_disposed)
{
if (disposing)
{
Close();
_envelope = null;
_tree = null;
}
_disposed = true;
}
}
/// <summary>
/// Creates a node and either splits the objects recursively into sub-nodes, or stores them at the node depending on the heuristics.
/// Tree is built top->down
/// </summary>
/// <param name="objList">Geometries to index</param>
/// <param name="depth">Current depth of tree</param>
/// <param name="heurdata">Heuristics data</param>
public QuadTree(List<BoxObjects> objList, uint depth, Heuristic heurdata)
{
_depth = depth;
_box = objList[0].Box;
for (int i = 0; i < objList.Count; i++)
_box = _box.Join(objList[i].Box);
// test our build heuristic - if passes, make children
if (depth < heurdata.Maxdepth && objList.Count > heurdata.Mintricnt &&
(objList.Count > heurdata.Tartricnt || ErrorMetric(_box) > heurdata.Minerror))
{
List<BoxObjects>[] objBuckets = new List<BoxObjects>[2]; // buckets of geometries
objBuckets[0] = new List<BoxObjects>();
objBuckets[1] = new List<BoxObjects>();
uint longaxis = _box.LongestAxis; // longest axis
double geoavg = 0; // geometric average - midpoint of ALL the objects
// go through all bbox and calculate the average of the midpoints
double frac = 1.0f/objList.Count;
for (int i = 0; i < objList.Count; i++)
geoavg += objList[i].Box.GetCentroid()[longaxis]*frac;
// bucket bbox based on their midpoint's side of the geo average in the longest axis
for (int i = 0; i < objList.Count; i++)
objBuckets[geoavg > objList[i].Box.GetCentroid()[longaxis] ? 1 : 0].Add(objList[i]);
//If objects couldn't be splitted, just store them at the leaf
//TODO: Try splitting on another axis
if (objBuckets[0].Count == 0 || objBuckets[1].Count == 0)
{
_child0 = null;
_child1 = null;
// copy object list
_objList = objList;
}
else
{
// create new children using the buckets
_child0 = new QuadTree(objBuckets[0], depth + 1, heurdata);
_child1 = new QuadTree(objBuckets[1], depth + 1, heurdata);
}
}
else
{
// otherwise the build heuristic failed, this is
// set the first child to null (identifies a leaf)
_child0 = null;
_child1 = null;
// copy object list
_objList = objList;
}
}
/// <summary>
/// Saves a node to a stream recursively
/// </summary>
/// <param name="node">Node to save</param>
/// <param name="sw">Reference to BinaryWriter</param>
private void SaveNode(QuadTree node, ref BinaryWriter sw)
{
//Write node boundingbox
sw.Write(node.Box.Min.X);
sw.Write(node.Box.Min.Y);
sw.Write(node.Box.Max.X);
sw.Write(node.Box.Max.Y);
sw.Write(node.IsLeaf);
if (node.IsLeaf)
{
sw.Write(node._objList.Count); //Write number of features at node
for (int i = 0; i < node._objList.Count; i++) //Write each featurebox
{
sw.Write(node._objList[i].Box.Min.X);
sw.Write(node._objList[i].Box.Min.Y);
sw.Write(node._objList[i].Box.Max.X);
sw.Write(node._objList[i].Box.Max.Y);
sw.Write(node._objList[i].Id);
}
}
else if (!node.IsLeaf) //Save next node
{
SaveNode(node.Child0, ref sw);
SaveNode(node.Child1, ref sw);
}
}
/// <summary>
/// Recursive function that traverses the tree and looks for intersections with a boundingbox
/// </summary>
/// <param name="box">Boundingbox to intersect with</param>
/// <param name="node">Node to search from</param>
/// <param name="list">List of found intersections</param>
private void IntersectTreeRecursive(BoundingBox box, QuadTree node, ref Collection<uint> list)
{
if (node.IsLeaf) //Leaf has been reached
{
foreach (BoxObjects boxObject in node._objList)
{
if(box.Intersects(boxObject.Box))
list.Add(boxObject.Id);
}
}
else
{
if (node.Box.Intersects(box))
{
IntersectTreeRecursive(box, node.Child0, ref list);
IntersectTreeRecursive(box, node.Child1, ref list);
}
}
}
/// <summary>
/// Reads a node from a stream recursively
/// </summary>
/// <param name="depth">Current depth</param>
/// <param name="br">Binary reader reference</param>
/// <returns></returns>
private static QuadTree ReadNode(uint depth, ref BinaryReader br)
{
QuadTree node = new QuadTree
{
_depth = depth,
Box = new BoundingBox(br.ReadDouble(), br.ReadDouble(), br.ReadDouble(), br.ReadDouble())
};
var isLeaf = br.ReadBoolean();
if (isLeaf)
{
int featureCount = br.ReadInt32();
node._objList = new List<BoxObjects>();
for (int i = 0; i < featureCount; i++)
{
BoxObjects box = new BoxObjects
{
Box = new BoundingBox(
br.ReadDouble(), br.ReadDouble(),
br.ReadDouble(), br.ReadDouble()),
Id = (uint) br.ReadInt32()
};
node._objList.Add(box);
}
}
else
{
node.Child0 = ReadNode(node._depth + 1, ref br);
node.Child1 = ReadNode(node._depth + 1, ref br);
}
return node;
}
/// <summary>
/// Disposes the node
/// </summary>
public void Dispose()
{
//this._box = null;
_child0 = null;
_child1 = null;
_objList = null;
}