GEANT321/ggeom/gnohyp.F

   1 *
   2 * $Id$
   3 *
   4 * $Log$
   5 * Revision 1.1.1.1  1995/10/24 10:20:52  cernlib
   6 * Geant
   7 *
   8 *
   9 #include "geant321/pilot.h"
  10 *CMZ :  3.21/02 29/03/94  15.41.29  by  S.Giani
  11 *-- Author :
  12       SUBROUTINE GNOHYP (X, PAR, IACT, SNEXT, SNXT, SAFE)
  13 C.
  14 C.    ******************************************************************
  15 C.    *                                                                *
  16 C.    *      COMPUTE DISTANCE UP TO INTERSECTION WITH HYPErboloid      *
  17 C.    *      VOLUME, FROM OUTSIDE POINT X(1-3) ALONG DIRECTION X(4-6)  *
  18 C.    *                                                                *
  19 C.    *       PAR   (input)  : volume parameters                       *
  20 C.    *                        inner radius                            *
  21 C.    *                        outer radius                            *
  22 C.    *                        half length in z                        *
  23 C.    *                        straw stereo angle in degrees           *
  24 C.    *                        r**2 = (z*tan(theta))**2 + a**2         *
  25 C.    *                                                                *
  26 C.    *       IACT  (input)  : action flag                             *
  27 C.    *         = 0  Compute SAFE only                                 *
  28 C.    *         = 1  Compute SAFE, and SNXT only if SNEXT .GT.new SAFE *
  29 C.    *         = 2  Compute both SAFE and SNXT                        *
  30 C.    *         = 3  Compute SNXT only                                 *
  31 C.    *       SNEXT (input)  : see IACT = 1                            *
  32 C.    *       SNXT  (output) : distance to volume boundary             *
  33 C.    *       SAFE  (output) : shortest distance to any boundary       *
  34 C.    *                                                                *
  35 C.    *    ==>Called by : GNEXT, GTNEXT                                *
  36 C.    *         Authors  M.J.Corden, A.Palounek                        *
  37 C.    *                                                                *
  38 C.    ******************************************************************
  39 C.
  40 #include "geant321/gconsp.inc"
  41       DIMENSION X(6),PAR(4),ENDR(2)
  42 *
  43 *     ------------------------------------------------------------------
  44 *
  45       SNXT = BIG
  46       TANTHS= (TAN(PAR(4)*DEGRAD))**2
  47       R2 = X(1)*X(1)+X(2)*X(2)
  48       ENDR(1)=SQRT(PAR(1)**2+PAR(3)**2*TANTHS)
  49       ENDR(2)=SQRT(PAR(2)**2+PAR(3)**2*TANTHS)
  50       SAF3=ABS(X(3))-PAR(3)
  51 *
  52       IF(IACT.EQ.3) GO TO 10
  53 *
  54 *     compute SAFE from escribed cylinders
  55 *
  56       R  = SQRT(R2)
  57       SAF1=PAR(1)-R
  58       SAF2=R-ENDR(2)
  59       SAFE = MAX(0.,SAF1,SAF2,SAF3)
  60 *
  61       IF(IACT.EQ.0) GO TO 999
  62       IF(IACT.EQ.1.AND.SAFE.GT.SNEXT) GO TO 999
  63 *
  64    10 CONTINUE
  65 *
  66 * *** Compute SNXT
  67 *
  68       IF((SAF3.GT.0.).AND.(X(3)*X(6).GE.0.)) GO TO 999
  69 C
  70 C       Compute intercept with inner & outer surfaces.
  71 C
  72       A = X(4)**2 + X(5)**2 - X(6)**2*TANTHS
  73       B = X(1)*X(4) + X(2)*X(5) - X(3)*X(6)*TANTHS
  74 C
  75       DO 30 NCYL =1,2
  76          C = R2 - X(3)**2*TANTHS - PAR(NCYL)**2
  77          SURD = B**2 - A*C
  78          IF(SURD.LE.0.0) GO TO 30
  79          SURD=SQRT(SURD)
  80 *
  81          DO 20 IR=-1,+1,2
  82             S=(-B+IR*SURD)/A
  83             IF((S.LT.0.).OR.(S.GT.SNXT)) GO TO 20
  84 *       Intersection point
  85             ZI = X(3) + S*X(6)
  86 *       Check Z limits
  87             IF(ABS(ZI).GT.PAR(3)) GO TO 20
  88 *       Intersection with hyperboloid ok
  89             SNXT = S
  90    20    CONTINUE
  91    30 CONTINUE
  92 *
  93 * *** Intersection with Z end planes
  94 *
  95       IF(SAF3.LE.0.) GO TO 999
  96       S    = SAF3/ABS(X(6))
  97 *     Intersection point
  98       XI  = X(1) + S*X(4)
  99       YI  = X(2) + S*X(5)
 100 *     Check R limits
 101       RI  = SQRT(XI*XI + YI*YI)
 102       IF(RI.LT.ENDR(1).OR.RI.GT.ENDR(2)) GO TO 999
 103 *     Intersection with Z end plane ok
 104       SNXT  = S
 105 *
 106   999 END