sPHENIX tracking discussion

[Christof Roland <Christof.Roland AT cern.ch>]

Hi Everybody, Evgeny,

after the discussion we had in the calibrations meeting yesterday I checked 
again how the phi position calculation in the TpcClusterizer is performed. 
See workflow below. We are currently still using a hardwired parametric 
approach in PHG4TpcCylinderGeom, I dont think this is what we want to 
proceed. 
We need to replace all the plethora of PHG4TpcCylinderGeom::get_phi* methods 
to use the pad plane coordinate lookup Evgeny is implementing.

int PHG4TpcCylinderGeom::get_phibins() const
PHG4TpcCylinderGeom::get_phistep() const
PHG4TpcCylinderGeom::get_phimin() const
PHG4TpcCylinderGeom::get_phibounds(const int ibin) const
int PHG4TpcCylinderGeom::get_phibin_new(const double phi) const
int PHG4TpcCylinderGeom::get_phibin(const double phi, int side) const
PHG4TpcCylinderGeom::get_phicenter_new(const int ibin) const
PHG4TpcCylinderGeom::get_phicenter(const int ibin) const
PHG4TpcCylinderGeom::get_phi(const float ibin) const


A cleaner way would probably be to keep the local x coordinate of the cluster 
in pad number coordinates and do the phi and global coordinate conversion
in the ACTS measuremenet conversion. 

We should discuss this in the next tracking meeting.

Cheers

   Christof 

Clusterizer Position extraction sketch:

double clusiphi = iphi_sum / adc_sum; <= weighted mean of pad number 
coordinates
double clusphi = my_data.layergeom->get_phi(clusiphi);

 thread_pair.data.layergeom = PHG4TpcCylinderGeom

PHG4TpcCylinderGeom::get_phi(const float ibin) const
{
  // double phi_center = -999;
  if (ibin < 0 || ibin > nphibins)
  {
        std::cout << PHWHERE << "Asking for invalid bin in phi: " << ibin << 
std::endl;
        exit(1);
  }

  check_binning_method_phi();

  const int side = 0;
  unsigned int pads_per_sector = nphibins / 12;
  unsigned int sector = ibin / pads_per_sector;
  double phi = (sector_max_Phi[side][sector] - (ibin + 0.5 - sector * 
pads_per_sector) * phistep);
  if (phi <= -M_PI)
  {
        phi += 2 * M_PI;
  }
  return phi;
}