This routine follows a track stored in /ZTSTA/ through the detector geometry stored in /ZTBAR/ and/or /FORWARD/ and calculates track parameters and their weight and covariance matrices on a surface stored in /ZTSEL/.
INCR : TRUE : transport the input weight matrix in /MATRIX/ along the track. Else : build the matrix from scratch.
IERR : error flag : 0 - no error 2 - track turns back before reference surface
from /ZTSTA/ : PMOM, THETA, PHI0 and AMASS : momentum direction and mass of particle at vertex ; ZVRTX : z-position of vertex; BFIELD : magnetic field [T]. from /ZTTRJ/ : IREF : the type of reference surface (1 = cylinder, 2 = plane).
from /ZTAUX/ : COTTH,TANTH : Cot and tan (theta) of track; RTRK,RINV : radius of track, and it's inverse; BCONST : c*BFIELD; PINV : inverse of momentum;
(To calculate weight matrix.)
(To invert weight matrix.)