ThirdHitPrediction.cc

Go to the documentation of this file.

#include "DataFormats/GeometryVector/interface/GlobalPoint.h"
#include "MagneticField/Engine/interface/MagneticField.h"
#include "RecoPixelVertexing/PixelLowPtUtilities/interface/ThirdHitPrediction.h"
#include "RecoPixelVertexing/PixelTrackFitting/interface/CircleFromThreePoints.h"
#include "RecoTracker/TkMSParametrization/interface/MultipleScatteringParametrisationMaker.h"
#include "RecoTracker/TkMSParametrization/interface/MultipleScatteringParametrisation.h"
#include "TrackingTools/DetLayers/interface/BarrelDetLayer.h"
#include "TrackingTools/DetLayers/interface/DetLayer.h"
#include "TrackingTools/DetLayers/interface/ForwardDetLayer.h"
#include "TrackingTools/Records/interface/TransientRecHitRecord.h"
#include "TrackingTools/TransientTrackingRecHit/interface/TransientTrackingRecHitBuilder.h"

inline float sqr(float x) { return x * x; }

using namespace std;

/*****************************************************************************/
ThirdHitPrediction::ThirdHitPrediction(const TrackingRegion& region,
                                       GlobalPoint inner,
                                       GlobalPoint outer,
                                       const MagneticField& magfield,
                                       const TransientTrackingRecHitBuilder& ttrhBuilder,
                                       double nSigMultipleScattering,
                                       double maxAngleRatio) {
  using namespace edm;
  theTTRecHitBuilder = &ttrhBuilder;

  Bz = fabs(magfield.inInverseGeV(GlobalPoint(0, 0, 0)).z());

  c0 = Global2DVector(region.origin().x(), region.origin().y());

  r0 = region.originRBound();
  rm = region.ptMin() / Bz;

  g1 = inner;
  g2 = outer;

  p1 = Global2DVector(g1.x(), g1.y());
  p2 = Global2DVector(g2.x(), g2.y());

  dif = p1 - p2;

  // Prepare circles of minimal pt (rm) and cylinder of origin (r0)
  keep = true;
  arc_0m = findArcIntersection(findMinimalCircles(rm), findTouchingCircles(r0), keep);

  nSigma = nSigMultipleScattering;
  maxRatio = maxAngleRatio;
}

/*****************************************************************************/
ThirdHitPrediction::~ThirdHitPrediction() {}

/*****************************************************************************/
void ThirdHitPrediction::invertCircle(Global2DVector& c, float& r) {
  float s = dif.mag2() / ((c - p1).mag2() - sqr(r));

  c = p1 + (c - p1) * s;
  r *= fabsf(s);
}

/*****************************************************************************/
void ThirdHitPrediction::invertPoint(Global2DVector& p) {
  float s = dif.mag2() / (p - p1).mag2();

  p = p1 + (p - p1) * s;
}

/*****************************************************************************/
pair<float, float> ThirdHitPrediction::findMinimalCircles(float r) {
  pair<float, float> a(0., 0.);

  if (dif.mag2() < 2 * sqr(r))
    a = pair<float, float>(dif.phi(), 0.5 * acos(1 - 0.5 * dif.mag2() / sqr(r)));

  return a;
}

/*****************************************************************************/
pair<float, float> ThirdHitPrediction::findTouchingCircles(float r) {
  Global2DVector c = c0;
  invertCircle(c, r);

  pair<float, float> a(0., 0.);
  a = pair<float, float>((c - p2).phi(), 0.5 * acos(1 - 2 * sqr(r) / (c - p2).mag2()));

  return a;
}

/*****************************************************************************/
pair<float, float> ThirdHitPrediction::findArcIntersection(pair<float, float> a, pair<float, float> b, bool& keep) {
  // spin closer
  while (b.first < a.first - M_PI)
    b.first += 2 * M_PI;
  while (b.first > a.first + M_PI)
    b.first -= 2 * M_PI;

  float min, max;

  if (a.first - a.second > b.first - b.second)
    min = a.first - a.second;
  else {
    min = b.first - b.second;
    keep = false;
  }

  if (a.first + a.second < b.first + b.second)
    max = a.first + a.second;
  else {
    max = b.first + b.second;
    keep = false;
  }

  pair<float, float> c(0., 0.);

  if (min < max) {
    c.first = 0.5 * (max + min);
    c.second = 0.5 * (max - min);
  }

  return c;
}

/*****************************************************************************/
void ThirdHitPrediction::fitParabola(const float x[3], const float y[3], float par[3]) {
  float s2 = sqr(x[0]) * (y[1] - y[2]) + sqr(x[1]) * (y[2] - y[0]) + sqr(x[2]) * (y[0] - y[1]);

  float s1 = x[0] * (y[1] - y[2]) + x[1] * (y[2] - y[0]) + x[2] * (y[0] - y[1]);

  float s3 = (x[0] - x[1]) * (x[1] - x[2]) * (x[2] - x[0]);
  float s4 =
      x[0] * x[1] * y[2] * (x[0] - x[1]) + x[0] * y[1] * x[2] * (x[2] - x[0]) + y[0] * x[1] * x[2] * (x[1] - x[2]);

  par[2] = s1 / s3;   // a2
  par[1] = -s2 / s3;  // a1
  par[0] = -s4 / s3;  // a0
}

/*****************************************************************************/
void ThirdHitPrediction::findRectangle(
    const float x[3], const float y[3], const float par[3], float phi[2], float z[2]) {
  // Initial guess
  phi[0] = min(x[0], x[2]);
  z[0] = min(y[0], y[2]);
  phi[1] = max(x[0], x[2]);
  z[1] = max(y[0], y[2]);

  // Extremum: position and value
  float xe = -par[1] / (2 * par[2]);
  float ye = par[0] - sqr(par[1]) / (4 * par[2]);

  // Check if extremum is inside the phi range
  if (phi[0] < xe && xe < phi[1]) {
    if (ye < z[0])
      z[0] = ye;
    if (ye > z[1])
      z[1] = ye;
  }
}

/*****************************************************************************/
float ThirdHitPrediction::areaParallelogram(const Global2DVector& a, const Global2DVector& b) {
  return a.x() * b.y() - a.y() * b.x();
}

/*****************************************************************************/
float ThirdHitPrediction::angleRatio(const Global2DVector& p3, const Global2DVector& c) {
  float rad2 = (p1 - c).mag2();

  float a12 = asin(fabsf(areaParallelogram(p1 - c, p2 - c)) / rad2);
  float a23 = asin(fabsf(areaParallelogram(p2 - c, p3 - c)) / rad2);

  return a23 / a12;
}

/*****************************************************************************/
void ThirdHitPrediction::spinCloser(float phi[3]) {
  while (phi[1] < phi[0] - M_PI)
    phi[1] += 2 * M_PI;
  while (phi[1] > phi[0] + M_PI)
    phi[1] -= 2 * M_PI;

  while (phi[2] < phi[1] - M_PI)
    phi[2] += 2 * M_PI;
  while (phi[2] > phi[1] + M_PI)
    phi[2] -= 2 * M_PI;
}

/*****************************************************************************/
void ThirdHitPrediction::calculateRangesBarrel(float r3, float phi[2], float z[2], bool keep) {
  pair<float, float> arc_all = findArcIntersection(arc_0m, findTouchingCircles(r3), keep);

  if (arc_all.second != 0.) {
    Global2DVector c3(0., 0.);  // barrel at r3
    invertCircle(c3, r3);       // inverted

    float angle[3];  // prepare angles
    angle[0] = arc_all.first - arc_all.second;
    angle[1] = arc_all.first;
    angle[2] = arc_all.first + arc_all.second;

    float phi3[3], z3[3];
    Global2DVector delta = c3 - p2;

    for (int i = 0; i < 3; i++) {
      Global2DVector vec(cos(angle[i]), sin(angle[i]));  // unit vector
      float lambda = delta * vec - sqrt(sqr(delta * vec) - delta * delta + sqr(r3));

      Global2DVector p3 = p2 + lambda * vec;  // inverted third hit
      invertPoint(p3);                        // third hit
      phi3[i] = p3.phi();                     // phi of third hit

      float ratio;

      if (keep && i == 1) {  // Straight line
        ratio = (p2 - p3).mag() / (p1 - p2).mag();
      } else {                                            // Circle
        Global2DVector c = p2 - vec * (vec * (p2 - p1));  // inverted antipodal
        invertPoint(c);                                   // antipodal
        c = 0.5 * (p1 + c);                               // center

        ratio = angleRatio(p3, c);
      }

      z3[i] = g2.z() + (g2.z() - g1.z()) * ratio;  // z of third hit
    }

    spinCloser(phi3);

    // Parabola on phi - z
    float par[3];
    fitParabola(phi3, z3, par);
    findRectangle(phi3, z3, par, phi, z);
  }
}

/*****************************************************************************/
void ThirdHitPrediction::calculateRangesForward(float z3, float phi[2], float r[2], bool keep) {
  float angle[3];  // prepare angles
  angle[0] = arc_0m.first - arc_0m.second;
  angle[1] = arc_0m.first;
  angle[2] = arc_0m.first + arc_0m.second;

  float ratio = (z3 - g2.z()) / (g2.z() - g1.z());

  if (0 < ratio && ratio < maxRatio) {
    float phi3[3], r3[3];

    for (int i = 0; i < 3; i++) {
      Global2DVector p3;

      if (keep && i == 1) {  // Straight line
        p3 = p2 + ratio * (p2 - p1);
      } else {                                             // Circle
        Global2DVector vec(cos(angle[i]), sin(angle[i]));  // unit vector

        Global2DVector c = p2 - vec * (vec * (p2 - p1));  // inverted antipodal
        invertPoint(c);                                   // antipodal
        c = 0.5 * (p1 + c);                               // center

        float rad2 = (p1 - c).mag2();

        float a12 = asin(areaParallelogram(p1 - c, p2 - c) / rad2);
        float a23 = ratio * a12;

        p3 = c + Global2DVector((p2 - c).x() * cos(a23) - (p2 - c).y() * sin(a23),
                                (p2 - c).x() * sin(a23) + (p2 - c).y() * cos(a23));
      }

      phi3[i] = p3.phi();
      r3[i] = p3.mag();
    }

    spinCloser(phi3);

    // Parabola on phi - z
    float par[3];
    fitParabola(phi3, r3, par);
    findRectangle(phi3, r3, par, phi, r);
  }
}

/*****************************************************************************/
void ThirdHitPrediction::calculateRanges(float rz3, float phi[2], float rz[2]) {
  // Clear
  phi[0] = 0.;
  rz[0] = 0.;
  phi[1] = 0.;
  rz[1] = 0.;

  // Calculate
  if (theBarrel)
    calculateRangesBarrel(rz3, phi, rz, keep);
  else
    calculateRangesForward(rz3, phi, rz, keep);
}

/*****************************************************************************/
void ThirdHitPrediction::getRanges(const DetLayer* layer, float phi[], float rz[]) {
  theLayer = layer;

  if (layer)
    initLayer(layer);

  float phi_inner[2], rz_inner[2];
  calculateRanges(theDetRange.min(), phi_inner, rz_inner);

  float phi_outer[2], rz_outer[2];
  calculateRanges(theDetRange.max(), phi_outer, rz_outer);

  if ((phi_inner[0] == 0. && phi_inner[1] == 0.) || (phi_outer[0] == 0. && phi_outer[1] == 0.)) {
    phi[0] = 0.;
    phi[1] = 0.;

    rz[0] = 0.;
    rz[1] = 0.;
  } else {
    while (phi_outer[0] > phi_inner[0] + M_PI) {
      phi_outer[0] -= 2 * M_PI;
      phi_outer[1] -= 2 * M_PI;
    }

    while (phi_outer[0] < phi_inner[0] - M_PI) {
      phi_outer[0] += 2 * M_PI;
      phi_outer[1] += 2 * M_PI;
    }

    phi[0] = min(phi_inner[0], phi_outer[0]);
    phi[1] = max(phi_inner[1], phi_outer[1]);

    rz[0] = min(rz_inner[0], rz_outer[0]);
    rz[1] = max(rz_inner[1], rz_outer[1]);
  }
}

/*****************************************************************************/
void ThirdHitPrediction::getRanges(float rz3, float phi[], float rz[]) { calculateRanges(rz3, phi, rz); }

/*****************************************************************************/
bool ThirdHitPrediction::isCompatibleWithMultipleScattering(GlobalPoint g3,
                                                            const vector<const TrackingRecHit*>& h,
                                                            vector<GlobalVector>& globalDirs,
                                                            const MultipleScatteringParametrisationMaker& msmaker) {
  Global2DVector p1(g1.x(), g1.y());
  Global2DVector p2(g2.x(), g2.y());
  Global2DVector p3(g3.x(), g3.y());

  CircleFromThreePoints circle(g1, g2, g3);

  if (circle.curvature() != 0.) {
    Global2DVector c(circle.center().x(), circle.center().y());

    float rad2 = (p1 - c).mag2();
    float a12 = asin(fabsf(areaParallelogram(p1 - c, p2 - c)) / rad2);
    float a23 = asin(fabsf(areaParallelogram(p2 - c, p3 - c)) / rad2);

    float slope = (g2.z() - g1.z()) / a12;

    float rz3 = g2.z() + slope * a23;
    float delta_z = g3.z() - rz3;

    // Transform to tt
    vector<TransientTrackingRecHit::RecHitPointer> th;
    for (vector<const TrackingRecHit*>::const_iterator ih = h.begin(); ih != h.end(); ih++)
      th.push_back(theTTRecHitBuilder->build(*ih));

    float sigma1_le2 = max(th[0]->parametersError()[0][0], th[0]->parametersError()[1][1]);
    float sigma2_le2 = max(th[1]->parametersError()[0][0], th[1]->parametersError()[1][1]);

    float sigma_z2 = (1 + a23 / a12) * (1 + a23 / a12) * sigma2_le2 + (a23 / a12) * (a23 / a12) * sigma1_le2;

    float cotTheta = slope * circle.curvature();  // == sinhEta
    float coshEta = sqrt(1 + sqr(cotTheta));      // == 1/sinTheta

    float pt = Bz / circle.curvature();
    float p = pt * coshEta;

    float m_pi = 0.13957018;
    float beta = p / sqrt(sqr(p) + sqr(m_pi));

    MultipleScatteringParametrisation msp = msmaker.parametrisation(theLayer);
    PixelRecoPointRZ rz2(g2.perp(), g2.z());

    float sigma_z = msp(pt, cotTheta, rz2) / beta;

    // Calculate globalDirs
    float sinTheta = 1. / coshEta;
    float cosTheta = cotTheta * sinTheta;

    int dir;
    if (areaParallelogram(p1 - c, p2 - c) > 0)
      dir = 1;
    else
      dir = -1;

    float curvature = circle.curvature();

    {
      Global2DVector v = (p1 - c) * curvature * dir;
      globalDirs.push_back(GlobalVector(-v.y() * sinTheta, v.x() * sinTheta, cosTheta));
    }

    {
      Global2DVector v = (p2 - c) * curvature * dir;
      globalDirs.push_back(GlobalVector(-v.y() * sinTheta, v.x() * sinTheta, cosTheta));
    }

    {
      Global2DVector v = (p3 - c) * curvature * dir;
      globalDirs.push_back(GlobalVector(-v.y() * sinTheta, v.x() * sinTheta, cosTheta));
    }

    // Multiple scattering
    float sigma_ms = sigma_z * coshEta;

    // Local error squared
    float sigma_le2 = max(th[2]->parametersError()[0][0], th[2]->parametersError()[1][1]);

    return (delta_z * delta_z / (sigma_ms * sigma_ms + sigma_le2 + sigma_z2) < nSigma * nSigma);
  }

  return false;
}

/*****************************************************************************/
void ThirdHitPrediction::initLayer(const DetLayer* layer) {
  if (layer->location() == GeomDetEnumerators::barrel) {
    theBarrel = true;
    theForward = false;
    const BarrelDetLayer& bl = dynamic_cast<const BarrelDetLayer&>(*layer);
    float halfThickness = bl.surface().bounds().thickness() / 2;
    float radius = bl.specificSurface().radius();
    theDetRange = Range(radius - halfThickness, radius + halfThickness);
  } else if (layer->location() == GeomDetEnumerators::endcap) {
    theBarrel = false;
    theForward = true;
    const ForwardDetLayer& fl = dynamic_cast<const ForwardDetLayer&>(*layer);
    float halfThickness = fl.surface().bounds().thickness() / 2;
    float zLayer = fl.position().z();
    theDetRange = Range(zLayer - halfThickness, zLayer + halfThickness);
  }
}