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// $Id: HelixIntersector.cc,v 1.3 2009/03/20 13:33:19 loizides Exp $
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#include "MitCommon/MathTools/interface/HelixIntersector.h"
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#include <iostream>
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ClassImp(mithep::HelixIntersector)
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using namespace std;
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using namespace mithep;
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//--------------------------------------------------------------------------------------------------
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HelixIntersector::HelixIntersector(const TVectorD *tr1, const TVector3 *momentum1,
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const TVectorD *tr2, const TVector3 *momentum2) :
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fISec0(tr1,momentum1,tr2,momentum2),
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fISec1(tr1,momentum1,tr2,momentum2)
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{
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// Constructor.
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// short cuts
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TrackParams &trk0 = fISec0.fTrk0;
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TrackParams &trk1 = fISec0.fTrk1;
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fISecs[0] = &fISec0;
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fISecs[1] = &fISec1;
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// Calculate intersections and test for existence
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// line connecting the two centers
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TVector3 connector = trk1.Center() - trk0.Center();
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// intersection positions relative to connector
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double para = (connector.Mag2()+trk0.Radius()*trk0.Radius()
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-trk1.Radius()*trk1.Radius())/(2.0*connector.Mag());
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double perpsqr = trk0.Radius()*trk0.Radius() - para*para;
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// intersection exist if perp is real -> perp^2 is positive
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fHasIntersections = (perpsqr >= 0.0);
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// fill Intersection objects appropriately
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if (fHasIntersections) {
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// vector perpendicular to connector (sign doesn't matter)
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TVector3 perpvec(connector.y(),-connector.x(),0.0);
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perpvec.SetMag(sqrt(perpsqr));
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// make both combinations
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for (int i = 0; i < 2; i++) {
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// the intersection
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fISecs[i]->fLocation =
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trk0.Center() + para * connector.Unit() + double(2*i-1) * perpvec;
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// calculate tracks/intersection specific quantities for real intersections both tracks have
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// the same point
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fISecs[i]->SetLocation(fISecs[i]->fLocation,fISecs[i]->fLocation);
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}
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if (fabs(fISecs[0]->DeltaZ()) > fabs(fISecs[1]->DeltaZ())) {
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Intersection* tmp = fISecs[1];
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fISecs[1] = fISecs[0];
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fISecs[0] = tmp;
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}
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}
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else {
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// no intersection so we pick points of closest approach
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TVector3 locTrk0 = trk0.Center() + trk0.Radius() * connector.Unit();
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TVector3 locTrk1 = trk1.Center() - trk1.Radius() * connector.Unit();
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// mean is the "nominal" location
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fISecs[0]->fLocation = (locTrk0 + locTrk1) * 0.5;
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// for closest approach points actually on the tracks are used calculate tracks/intersection
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// specific quantities
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fISecs[0]->SetLocation(locTrk0,locTrk1);
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}
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}
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//--------------------------------------------------------------------------------------------------
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HelixIntersector::~HelixIntersector()
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{
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// Destructor.
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}
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//--------------------------------------------------------------------------------------------------
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HelixIntersector::TrackParams::TrackParams(const TVectorD *trk, const TVector3 *momentum) :
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Helix ((*trk)(0),(*trk)(1),(*trk)(2),(*trk)(3),Angle((*trk)(4))),
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fTrkMom(*momentum)
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{
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// Calculate center of r-phi plane circles.
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double rho = Radius() + Helicity() * D0();
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double phi = Helicity() * M_PI/2.0 + Phi0();
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double z = 0.0;
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if (0 && rho < 0) {
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printf("Cylindrical coordinates supplied with negative Rho\n");
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printf("Radius = %5f, Helicity = %5f, D0 = %5f, Rho=%5f\n", Radius(), Helicity(), D0(), rho);
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}
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fCenter.SetXYZ(rho*cos(phi),rho*sin(phi),z);
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// Original code ....
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//fCenter.SetRhoPhiZ(Radius() + Helicity() * D0(),
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// Helicity() * M_PI/2.0 + Phi0(),0.0);
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}
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//--------------------------------------------------------------------------------------------------
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void HelixIntersector::TrackParams::SetLocation(TVector3& location)
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{
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// Rotation about circle center.
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double deltaphi = M_PI - fCenter.Angle(location-fCenter);
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// check for backward locations
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if (fTrkMom.Dot(location)<0.0)
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deltaphi = - deltaphi;
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// calculate arc length to and z of intersection
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fArcLen = Radius()*deltaphi/SinTheta();
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fZAtISec = Z0() + Radius()*deltaphi*CotTheta();
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// calculate momentum of track at intersection
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fMomentum = Direction(fArcLen) * fTrkMom.Mag();
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}
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//--------------------------------------------------------------------------------------------------
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HelixIntersector::Intersection::Intersection(const TVectorD *tr1, const TVector3 *momentum1,
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const TVectorD *tr2, const TVector3 *momentum2) :
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fDeltaZ(0.0),
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fTrk0 (tr1,momentum1),
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fTrk1 (tr2,momentum2)
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{
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// Constructor.
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fTrks[0] = &fTrk0;
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fTrks[1] = &fTrk1;
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}
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//--------------------------------------------------------------------------------------------------
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void HelixIntersector::Intersection::SetLocation(TVector3& loc1, TVector3& loc2)
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{
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// Calculate tracks specific quantities.
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fTrk0.SetLocation(loc1);
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fTrk1.SetLocation(loc2);
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// combined variables
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fDeltaZ = fTrk0.fZAtISec - fTrk1.fZAtISec;
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fLocation.SetZ((fTrk0.fZAtISec + fTrk1.fZAtISec)/2.0);
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fMomentum = fTrk0.fMomentum + fTrk1.fMomentum;
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}
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