4.4.58 SUBROUTINE ZTREFE(DSTR, IERR) : intersection with REFErence surface

This routine finds the point where the track stored in /ZTSTA/ and /ZTAUX/ intersects the reference surface stored in /ZTSEL/. The intersection point is stored in /ZTTRJ/, Uses fast, approximative tracking.

ARGUMENTS:

OUTPUT :

    DSTR : track length from vertex to intersection with reference surface.
    IERR : error flag :
             0 - no error
             2 - track turns back before reference surface

IMPLICIT INPUTS:

    from /ZTAUX/ : TANTH, RTRK, RINV : tan(theta), radius and 1/radius
                 of track (calculated elsewhere from values in /ZTSTA/)
    from /ZTSEL/ : RREF and ZREF : radius of reference surface (for
                 cylinder) or Z-coordinate ( for plane).
    from /ZTSTA/ : ZVRTX : z-position of vertex.

IMPLICIT OUTPUTS:

    to /ZTTRJ/ : R(0),Z(0),PHI(0),BETA(0) : track parameters at intersection
                point; IREF : type of intersection (1 = cylinder, 2=plane)

CALLED BY :

ZTFOLL, FOLLow track through detector (see 4.4.56).

CALLED ROUTINE(S):

none

SIDE EFFECTS:

none

AUTHORS:

P. Billoir , LPNHE

CREATION DATE:

27-jul-1992