R. Snider
							July 7, 1999
							

Silicon clustering module:  SiClusteringModule
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Synopsis:

    The silicon clustering module, SiClusteringModule, analyzes the strip
    data from the silicon detectors and produces a set of strip clusters
    that represent charge deposited by a single particle as it traverses
    the silicon, and a set of hits that represent the position information
    inferred from the cluster profile. 


Required inputs:

	SVX strip data:    SIXD bank
	ISL strip data:    ISLD bank
	Calibration data:  none currently required

	High-level interfaces:
	
	    SiStrip		- strip-level information
	    TRYRun2SiStripSet	- strip collection based upon contents of
	    			  SIXD and ISLD banks

Outputs:

	Hits and basic clusters:  QSIC bank
	Cluster profiles:         QSIP bank

	High-level interfaces: (all defined in TrackingSI package)
	
	    SiHit		- hit information
	    SiPhiHit		- representation of hit in phi strips
	    SiSasHit		- representation of hit in small-angle
	    			  stereo strips
	    SiZHit		- representation of hit in Z strips
	    SiHitSet		- hit collection
	    SiCluster		- cluster profile information
	    SiClusterSet	- cluster collection
	    StoredSiClusterData - provides access to SiHitSet and 
	    			  SiClusterSet objects based
				  upon contents of underlying banks

Talk-to options:

	No special talk-to commands are required.
	

Details:

    As particles traverse the silicon detector, they often deposit charge
    among several adjacent strips. The profile of the resulting "cluster"
    depends upon many factors, including the strip pitch, angle of
    incidence of the track, type of charge carrier,  diffusion of charge
    carriers in the silicon, and magnetic field to name a few. The
    clustering algorithm identifies groups of contiguous strips that
    represent the charge from a single particle.  Due to differences in the
    above factors across the detector,  the clustering algorithm and
    position calculation employed  may vary depending upon the particular
    readout element in question.

    SiClusteringModule defines a set of clustering objects, each of which
    applies to a particular detector element (one side of one
    half-ladder).  It is possible in principle to define a separate
    algorithm for each side of each half-ladder in the silicon detectors.
    In practice, the primary distinction is between those algorithms
    applied to 90-degree stereo strips and those applied to all other
    strips. Once a set of contiguous strips has been identified as a
    cluster, the position and resolution is calculated using a separate
    algorithm that is bound to the clustering object.

    At present, a single algorithm is used throughout the detector,
    although separate clustering objects are used for each side of each
    layer in the detector. The current algorithm seeks to divide every
    set of contiguous strips at all local minima. This procedure helps to
    improve the position resolution and reduces the deleterious effects of
    cluster overlaps for clusters in phi and small-angle stereo strips. 
    
    In the long term, this algorithm is not appropriate to deal with
    clusters in the 90-degree stereo strips produced by tracks in the
    forward or backward directions. It is adequate, however, for most
    tracks simulated using the (default) "GEOMETRICAL" charge deposition
    model. Performance will degrade significantly for forward and backward
    tracks simulated using the more realistic charge deposition models.


Access to output data:

    Note: The details of the following classes are discussed elsewhere.

    Cluster information, including the number of strips, total charge and
    cluster profile, are held within the SiCluster class. The position
    information associated with a cluster is held within the SiHit class.
    This division is necessary because some clusters have multiple
    positions associated with them.
    
    All clusters are held within an SiClusterSet object, ordered by
    detector element, then strip number of the first strip in the cluster.
    Hits are held within an SiHitSet object, again ordered by detector
    element, then position. For hits on phi and small-angle stereo strips,
    the hits are ordered by increasing global phi. For hits in Z-strips,
    the hits are ordered by increasing global Z. Both of these collections
    are managed by the StoredSiClusterData class, which reads the banks
    associated with cluster and hit information, creates the necessary
    low-level objects and fills the collections. All classes have formatted
    print methods and respond to the "<<" output operator.


Access to input data:

    Note: The details of the following classes are discussed elsewhere.
    
    Strip information, including the strip number and charge in ADC counts,
    is held by the SiStrip class. The strip data for an event can be
    unpacked from the raw data banks by using the TRYRun2SiStripSet class.
    This class derives from the SiStripSet class, which defines the
    interface by which users can access the strips themselves. Strips
    within this collection are ordered by detector element, then by
    increasing strip number, as defined by the readout system. All classes
    have formatted print methods and respond to the "<<" output operator.