getCircleParams treats as straight track with too small sagitta

If sagitta of between the beam-line and the middle of the TPC is <0.01cm,
treat the track as straight line instead of circle in XY.

Author: shahor02

DataFormats/Reconstruction/include/ReconstructionDataFormats/Track.h

@@ -348,7 +348,9 @@ inline void TrackPar::getCircleParamsLoc(float bz, o2::utils::CircleXY& c) const
 {
   // get circle params in track local frame, for straight line just set to local coordinates
   c.rC = getCurvature(bz);
-  if (std::abs(c.rC) > o2::constants::math::Almost0) {
+  // treat as straight track if sagitta between the vertex and middle of TPC is below 0.01 cm
+  constexpr float MinSagitta = 0.01, TPCMidR = 160., MinCurv = 8 * MinSagitta / (TPCMidR * TPCMidR);
+  if (std::abs(c.rC) > MinCurv) {
     c.rC = 1.f / getCurvature(bz);
     float sn = getSnp(), cs = sqrtf((1. - sn) * (1. + sn));
     c.xC = getX() - sn * c.rC; // center in tracking