Add new interface for track density helper tool

Former-commit-id: 275b8d4e47cef05435fffbd31410b10940cf744e

Tracking/TrkVertexFitter/TrkVertexFitterInterfaces/TrkVertexFitterInterfaces/IVertexTrackDensityEstimator.h

+/*
+  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+*/
+
+///////////////////////////////////////////////////////////////////
+// IVertexTrackDensityEstimator.h, (c) ATLAS Detector software 2018
+///////////////////////////////////////////////////////////////////
+
+#ifndef TRKVERTEXFITTERINTERFACE_IVERTEXTRACKDENSITYESTIMATOR_H
+#define TRKVERTEXFITTERINTERFACE_IVERTEXTRACKDENSITYESTIMATOR_H
+
+#include "GaudiKernel/IAlgTool.h"
+#include "TrkParameters/TrackParameters.h"
+
+/**
+ * @class Trk::IVertexTrackDensityEstimator
+ *
+ * An abstract base class for implementation of
+ * weight functions for seeding. Calculates the 
+ * the density of tracks at a given point along
+ * the beamline given a set of tracks. 
+ *
+ *@author Dave Casper (dcasper@uci.edu) 
+ *
+ * --------------------------------------------------------
+ */
+
+namespace Trk
+{
+  class Track;
+
+  static const InterfaceID IID_IVertexTrackDensityEstimator("IVertexTrackDensityEstimator", 1, 0);
+
+  class IVertexTrackDensityEstimator : virtual public IAlgTool {
+
+     public:
+       /**
+        *  Virtual destructor 
+	*/
+       virtual ~IVertexTrackDensityEstimator() {};
+
+       /** 
+        * AlgTool interface methods 
+	*/
+       static const InterfaceID& interfaceID() { return IID_IVertexTrackDensityEstimator; };
+
+
+       /**
+        *   Adds a list of tracks, whose impact parameters will contribute to the density function.
+        */
+       virtual void addTracks(const std::vector<const Trk::Track*>& vectorTrk) = 0;
+
+       /**
+	*  Adds a list of track perigee parameters, whose impact parameters will contribute to 
+        *  the density function.
+        */
+       virtual void addTracks(const std::vector<const Trk::TrackParameters*>& perigeeList) = 0;
+
+       /**
+        *  Removes a list of tracks, which will no longer contribute to the density function.
+        */
+       virtual void removeTracks(const std::vector<const Trk::Track*>& vectorTrk) = 0;
+
+       /**
+        *  Removes a list of track perigee parameters, which will no longer contribute to 
+        *  the density function.
+        */
+       virtual void removeTracks(const std::vector<const Trk::TrackParameters*>& perigeeList) = 0;
+
+       /**
+        *  Evaluate the density function at the specified coordinate along the beam-line.
+        */
+       virtual double trackDensity(double z) = 0;
+
+       /**
+        *  Resets the internal state of the tool, forgetting all tracks previously added.
+        */
+       virtual void reset() = 0;
+
+  };
+}
+
+#endif