public void RecalculateCentroid()
{
double n = (double)this.NumPoints();
if (n > 0)
{
double avgx = (from p in this.Points select p.x).Sum() / n;
double avgy = (from p in this.Points select p.y).Sum() / n;
this.Centroid = new kPoint(avgx, avgy);
}
}
/**
* Get the index of the closest cluster to a given point
*/
public static int GetNearestCluster(kPoint p, List <kCluster> Clusters)
{
double minDistance = double.MaxValue;
int nearestClusterIndex = -1;
for (int x = 0; x < Clusters.Count; x++)
{
// Calculate the distance to the current cluster
double distance = Math.Sqrt(Math.Pow(p.x - Clusters[x].Centroid.x, 2.0) + Math.Pow(p.y - Clusters[x].Centroid.y, 2.0));
// If this Cluster is closer than the previous closest
if (distance < minDistance)
{
// Set this cluster as the closest
nearestClusterIndex = x;
minDistance = distance;
}
}
return(nearestClusterIndex);
}
public static void kGeometryMeans(SqlGeometry MultiPoint, int k)
{
// Check that we aren't creating more clusters than points
if (MultiPoint.STNumPoints() < k)
{
throw new Exception("Number of clusters cannot be greater than number of points");
}
/**
* 1.) Initialisation Step
*/
// Create k empty clusters
List <kCluster> Clusters = new List <kCluster>();
for (int c = 0; c < k; c++)
{
// Each cluster starts as an empty collection centred at (0, 0)
Clusters.Add(new kCluster());
}
// Assign each point to an arbitrary initial cluster
int C = 0;
for (int n = 1; n <= MultiPoint.STNumPoints(); n++)
{
kPoint p = new kPoint((double)MultiPoint.STPointN(n).STX, (double)MultiPoint.STPointN(n).STY);
Clusters[C].AddPoint(p);
C++;
if (C >= Clusters.Count)
{
C = 0;
}
}
// Print some debug information
SqlContext.Pipe.Send("There are " + Clusters.Count + " clusters, containing a total of " + MultiPoint.STNumPoints() + " points.");
/**
* 2.) Assignment Step
* Loop through every point and assign them to their closest cluster
*/
// This variable will keep track of when to break the loop
bool convergancereached = false;
while (!convergancereached)
{
// On each iteration, assume points won't move clusters
convergancereached = true;
// Loop through every cluster
for (int c = 0; c < k; c++)
{
// Loop through every point in this cluster
for (int pointIndex = 0; pointIndex < Clusters[c].NumPoints(); pointIndex++)
{
// Retrieve this point
kPoint Point = Clusters[c].PointN(pointIndex);
// Determine the closest cluster for this point
int nearestCluster = GetNearestCluster(Point, Clusters);
// If this is not the cluster in which the point currently lies...
if (nearestCluster != c)
{
// Add the point to its nearest cluster
Clusters[nearestCluster].AddPoint(Point);
// And remove it from its previous cluster
Clusters[c].RemovePoint(Point);
// A point has changed clusters, so we need to continue iterating
convergancereached = false;
}
}
}
/**
* 3.) Update Step
* Compute the new centres of each cluster
*/
// foreach(Cluster c in Clusters)
for (int c = 0; c < Clusters.Count; c++)
{
Clusters[c].RecalculateCentroid();
}
}
/**
* OUTPUT
*/
// Use the first record to set the SRID
int srid = (int)MultiPoint.STSrid;
SqlMetaData[] columns = new SqlMetaData[3];
columns[0] = new SqlMetaData("ClusterID", SqlDbType.Int);
columns[1] = new SqlMetaData("Centroid", SqlDbType.Udt, typeof(SqlGeometry));
columns[2] = new SqlMetaData("Points", SqlDbType.Udt, typeof(SqlGeometry));
// Create a record object that represents an individual row, including it's metadata.
SqlDataRecord record = new SqlDataRecord(columns);
SqlContext.Pipe.SendResultsStart(record);
for (int c = 0; c < Clusters.Count; c++)
{
record.SetValue(0, c);
SqlGeometry Centroid = SqlGeometry.Point(Clusters[c].GetCentroid().x, Clusters[c].GetCentroid().y, srid);
record.SetValue(1, Centroid);
SqlGeometry Points = SqlGeometry.STGeomFromText(new SqlChars("GEOMETRYCOLLECTION EMPTY"), srid);
foreach (kPoint p in Clusters[c].GetPoints())
{
Points = Points.STUnion(SqlGeometry.Point(p.x, p.y, srid));
}
record.SetValue(2, Points);
SqlContext.Pipe.SendResultsRow(record);
}
SqlContext.Pipe.SendResultsEnd();
}
public void RemovePoint(kPoint p)
{
this.Points.Remove(p);
this.RecalculateCentroid();
}
public void AddPoint(kPoint p)
{
this.Points.Add(p);
this.RecalculateCentroid();
}
public void SetCentroid(kPoint p)
{
this.Centroid = p;
}
public kCluster()
{
this.Centroid = new kPoint();
this.Points = new List <kPoint>();
}
