getBestVertex.h

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#include "DataFormats/TrackReco/interface/Track.h"
#include "DataFormats/VertexReco/interface/Vertex.h"
#include "DataFormats/VertexReco/interface/VertexFwd.h"
#include <limits>
 
using Point = math::XYZPoint;
 
inline Point getBestVertex(reco::Track const& trk,
                           reco::VertexCollection const& vertices,
                           const size_t minNtracks = 2) {
  Point p_dz(0, 0, -99999);
  float dzmin = std::numeric_limits<float>::max();
  for (auto const& vertex : vertices) {
    size_t tracks = vertex.tracksSize();
    if (tracks < minNtracks) {
      continue;
    }
    float dz = std::abs(trk.dz(vertex.position()));
    if (dz < dzmin) {
      p_dz = vertex.position();
      dzmin = dz;
    }
  }
 
  return p_dz;
}
 
inline Point getBestVertex_withError(reco::Track const& trk,
                                     reco::VertexCollection const& vertices,
                                     Point& error,
                                     const size_t minNtracks = 2) {
  Point p_dz(0, 0, -99999);
  float dzmin = std::numeric_limits<float>::max();
  for (auto const& vertex : vertices) {
    size_t tracks = vertex.tracksSize();
    if (tracks < minNtracks) {
      continue;
    }
    float dz = std::abs(trk.dz(vertex.position()));
    if (dz < dzmin) {
      p_dz = vertex.position();
      error.SetXYZ(vertex.xError(), vertex.yError(), vertex.zError());
      dzmin = dz;
    }
  }
 
  return p_dz;
}