sfcnn is a general K-nearest neighbor search data structure.

sfcnn< MyPointType,
             Dimension,
             CoordType >
                      NN(&FirstDataPoint, Size);

• MyPointType
  
• This can be any user defined point type, as long as the
  coordinates can be referenced by the bracket operator.
  For example, vector<double> or float[], are both valid.
• Dimension  
  
• This is the dimension of the points in the data set.
• CoordType
• This is the type of coordinate the points use.
  Currently supported types are:
  (unsigned) short, int, long
  short, int, long
  float, double, long double
  
• IMPORTANT! Searches on integer types operate
  about 3x faster than floating point types.  If you
  can use them, it is recommended.
• FirstPoint
• A pointer to the first point in the input data set
• Size
• The size of the input data set

Queries are thread-safe and may be done in
parallel using openmp, posix threads, etc.

NN.ksearch(MyPointType Q,
                       int k,
                       vector<unsigned long> answer,
                       double epsilon)
or

NN.ksearch(MyPointType Q,
                       int k,
                       vector<unsigned long> answer,
                       vector<double> distance,
                       double epsilon)

• Q
• A query point of type MyPointType.
• k
• The number of nearest neighbors
  to return.  Ie. k=5 will return the 5
  nearest points to Q in the data set
  
• answer
•  This vector will contain the indexes
  of the k nearest data points.  These
  indexes are based off the FirstDataPoint
  given at initialization.  If the points have
  been moved, the indexes will be
  incorrect.
  
• distance
• This vector will contain the squared
  distance from the query point to the
  corresponding data point
  
  
• epsilon
• This parameter is optional, and defaults
  to 0. This approximation parmater garuntees
  that the distance to the farthest returned
  point is no farther than (1+eplsilon)*(distance
  to actual k nearest neighbor).  To compute
  an exact solution leave it to be 0.