/// <summary>
/// Searches the graph for nearby vertices assuming it has been sorted.
/// </summary>
/// <typeparam name="TEdgeData"></typeparam>
public static List <uint> SearchHilbert <TEdgeData>(this GraphBase <TEdgeData> graph, int n, float latitude, float longitude,
float offset)
where TEdgeData : struct, IGraphEdgeData
{
var targets = HilbertCurve.HilbertDistances(
System.Math.Max(latitude - offset, -90),
System.Math.Max(longitude - offset, -180),
System.Math.Min(latitude + offset, 90),
System.Math.Min(longitude + offset, 180), n);
targets.Sort();
var vertices = new List <uint>();
var targetIdx = 0;
var vertex1 = (uint)1;
var vertex2 = (uint)graph.VertexCount;
float vertexLat, vertexLon;
while (targetIdx < targets.Count)
{
uint vertex;
int count;
if (GraphExtensions.SearchHilbert(graph, targets[targetIdx], n, vertex1, vertex2, out vertex, out count))
{ // the search was successful.
while (count > 0)
{ // there have been vertices found.
if (graph.GetVertex((uint)vertex + (uint)(count - 1), out vertexLat, out vertexLon))
{ // the vertex was found.
if (System.Math.Abs(latitude - vertexLat) < offset &&
System.Math.Abs(longitude - vertexLon) < offset)
{ // within offset.
vertices.Add((uint)vertex + (uint)(count - 1));
}
}
count--;
}
// update vertex1.
vertex1 = vertex;
}
// move to next target.
targetIdx++;
}
return(vertices);
}
/// <summary>
/// Searches the graph for nearby vertices assuming it has been sorted.
/// </summary>
/// <typeparam name="TEdgeData"></typeparam>
public static bool SearchHilbert <TEdgeData>(this GraphBase <TEdgeData> graph, long hilbert, int n,
uint vertex1, uint vertex2, out uint vertex, out int count)
where TEdgeData : struct, IGraphEdgeData
{
var hilbert1 = GraphExtensions.HilbertDistance(graph, n, vertex1);
var hilbert2 = GraphExtensions.HilbertDistance(graph, n, vertex2);
while (vertex1 <= vertex2)
{
// check the current hilbert distances.
if (hilbert1 > hilbert2)
{ // situation is impossible and probably the graph is not sorted.
throw new Exception("Graph not sorted: Binary search using hilbert distance not possible.");
}
if (hilbert1 == hilbert)
{ // found at hilbert1.
var lower = vertex1;
while (hilbert1 == hilbert)
{
lower--;
if (lower == 0)
{ // stop here, not more vertices lower.
break;
}
hilbert1 = GraphExtensions.HilbertDistance(graph, n, lower);
}
lower++;
var upper = vertex1;
hilbert1 = GraphExtensions.HilbertDistance(graph, n, upper);
while (hilbert1 == hilbert)
{
upper++;
if (upper > graph.VertexCount)
{ // stop here, no more vertices higher.
break;
}
hilbert1 = GraphExtensions.HilbertDistance(graph, n, upper);
}
upper--;
vertex = lower;
count = (int)(upper - lower) + 1;
return(true);
}
if (hilbert2 == hilbert)
{ // found at hilbert2.
var lower = vertex2;
while (hilbert2 == hilbert)
{
lower--;
if (lower == 0)
{ // stop here, not more vertices lower.
break;
}
hilbert2 = GraphExtensions.HilbertDistance(graph, n, lower);
}
lower++;
var upper = vertex2;
hilbert2 = GraphExtensions.HilbertDistance(graph, n, upper);
while (hilbert2 == hilbert)
{
upper++;
if (upper > graph.VertexCount)
{ // stop here, no more vertices higher.
break;
}
hilbert2 = GraphExtensions.HilbertDistance(graph, n, upper);
}
upper--;
vertex = lower;
count = (int)(upper - lower) + 1;
return(true);
}
if (hilbert1 == hilbert2 ||
vertex1 == vertex2 ||
vertex1 == vertex2 - 1)
{ // search is finished.
vertex = vertex1;
count = 0;
return(true);
}
// Binary search: calculate hilbert distance of the middle.
var vertexMiddle = vertex1 + (uint)((vertex2 - vertex1) / 2);
var hilbertMiddle = GraphExtensions.HilbertDistance(graph, n, vertexMiddle);
if (hilbert <= hilbertMiddle)
{ // target is in first part.
vertex2 = vertexMiddle;
hilbert2 = hilbertMiddle;
}
else
{ // target is in the second part.
vertex1 = vertexMiddle;
hilbert1 = hilbertMiddle;
}
}
vertex = vertex1;
count = 0;
return(false);
}
/// <summary>
/// Searches the graph for nearby vertices assuming it has been sorted.
/// </summary>
/// <typeparam name="TEdgeData"></typeparam>
public static List <uint> SearchHilbert <TEdgeData>(this GraphBase <TEdgeData> graph, float latitude, float longitude,
float offset)
where TEdgeData : struct, IGraphEdgeData
{
return(GraphExtensions.SearchHilbert(graph, GraphExtensions.DefaultHilbertSteps, latitude, longitude, offset));
}
