class THaVDCPointPair: public TObject

 Compute goodness of match parameter between upper and lower point.
 Essentially, this is a measure of how closely the two local tracks
 point at each other.

 Mark upper and lower points as well as their clusters
 as belonging to the given track

 Calculate chi2 and number of data points for the associated track
 and clusters

 Compare this object to another THaVDCPointPair.
 Used for sorting tracks.

 Calculate projected positions of points in opposite planes, measure
 how far they differ from partner point intercept, and return the sum
 of the squares of the distances

 Project 'here' to plane of 'there' and return square of distance between
 projected position and intercept of 'there'

 Return track associated with this pair

 Return true if any cluster underlying this point pair is also part of
 another point pair that has already been chosen for making a track.
 This ensures each cluster is only ever used in at most one final track.

 Print details about this point pair (for debugging)

 Mark this point pair as used (i.e. chosen for making a track)
 This does the following:

 (a) upper and lower points are marked as each other's partners
 (b) the underlying four clusters are marked as associated with this pair
 (c) the global slope resulting from the coordinate pair is calculated
     and stored in the clusters associated with the points
 (d) This pair is marked as used

 Mark this track pair as unused