GEANT321/ggeom/gnhype.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 GNHYPE (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 INSIDE 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)
  42
  43 C-------------------------------------------------------------
  44
  45       SNXT = BIG
  46       R2   = X(1)*X(1) + X(2)*X(2)
  47       TANTHS=(TAN(PAR(4)*DEGRAD))**2
  48
  49 C       -------------------------------------------------
  50 C       |  Compute safety-distance 'SAFE' (P.Weidhaas)  |
  51 C       -------------------------------------------------
  52
  53       SAFZ1  = PAR(3) - X(3)
  54       SAFZ2  = PAR(3) + X(3)
  55
  56       IF (IACT .LT. 3) THEN
  57
  58 C    tube version:
  59 C      R    = SQRT (R2)
  60 C      IF (PAR(1).NE.0.) THEN
  61 C         SAFR1  = R - PAR(1)
  62 C      ELSE
  63 C         SAFR1  = BIG
  64 C      ENDIF
  65 C      SAFR2  = PAR(2) - R
  66 C
  67 C        SAFE  = MIN (SAFZ1, SAFZ2, SAFR1, SAFR2)
  68 C
  69 C    simple, safe choice for hyperboloid for now:
  70       SAFE=0.
  71 C
  72         IF (IACT .EQ. 0) GO TO 999
  73         IF (IACT .EQ. 1) THEN
  74           IF (SNEXT .LT. SAFE) GO TO 999
  75         ENDIF
  76       ENDIF
  77
  78 C     ------------------------------------------------
  79 C     |  Compute vector-distance 'SNXT' (McPherson)  |
  80 C     ------------------------------------------------
  81
  82 C
  83 C             Compute intersection with z-boundaries.
  84 C
  85       IF(X(6).GT.0.)THEN
  86          SNXT=SAFZ1/X(6)
  87       ELSEIF(X(6).LT.0.)THEN
  88          SNXT=-SAFZ2/X(6)
  89       ENDIF
  90 C
  91 C     Compute intercepts with inner & outer curved surfaces:
  92 C
  93       A = X(4)**2 + X(5)**2 - X(6)**2*TANTHS
  94       B = X(1)*X(4) + X(2)*X(5) - X(3)*X(6)*TANTHS
  95
  96       DO 38 NCYL =1,2
  97         C = R2 - X(3)**2*TANTHS - PAR(NCYL)**2
  98         SURD = B**2 - A*C
  99         IF(SURD.GT.0.) THEN
 100           SURD=SQRT(SURD)
 101           DIST1=(-B+SURD)/A
 102           IF(DIST1.GT.0.) SNXT=MIN(SNXT,DIST1)
 103           DIST2=(-B-SURD)/A
 104           IF(DIST2.GT.0.) SNXT=MIN(SNXT,DIST2)
 105 C       not necessary to compute intercept with outer surface
 106 C       if there is a positive intercept with inner surface:
 107           IF(DIST1.GT.0. .OR. DIST2.GT.0.) GO TO 999
 108         ENDIF
 109   38  CONTINUE
 110 C
 111  999  CONTINUE
 112       END