GEANT321/ggeom/gvlong.F

   1 *
   2 * $Id$
   3 *
   4 * $Log$
   5 * Revision 1.1.1.1  1995/10/24 10:20:57  cernlib
   6 * Geant
   7 *
   8 *
   9 #include "geant321/pilot.h"
  10 *CMZ :  3.21/02 29/03/94  15.41.31  by  S.Giani
  11 *-- Author :
  12 *
  13       SUBROUTINE GVLONG (DIR, C, NC, TAU, NTAU)
  14 ************************************************************************
  15 *                                                                      *
  16 * GVLONG calculates the distance to the surface along a      VP 920125 *
  17 *        given DIRection                                               *
  18 *                                                                      *
  19 *        SHOULD BE called ONLY AFTER call GVSAFE.                      *
  20 *        due to some results of GVSAFE are used.                       *
  21 *        Just by this reason starting XYZ point                        *
  22 *        is omitted                                                    *
  23 *        =======================================                       *
  24 *                                                                      *
  25 * Input  : DIR -   direction                                           *
  26 *          C   -   coeffs of surface (C(1) not used)                   *
  27 *          NC  -   number of coefs                                     *
  28 *                                                                      *
  29 * Output : TAU -   TAU(1:2) distances to surface in increasing order   *
  30 *                  in the units of the length of DIR                   *
  31 *          NTAU -  number of distances (solutions)  (0,1,2)            *
  32 *                                                                      *
  33 ************************************************************************
  34       COMMON /SLATE/ SLATE (40)
  35       INTEGER        ISLATE(40)
  36       EQUIVALENCE    (SLATE,ISLATE)
  37       REAL           C(*), DIR(3), TAU(2), CBA(3)
  38       LOGICAL        XLINE
  39 *-----------------------------------------------------------------------
  40 *
  41 *     SLATE(10) is the value of S(X) = equation of the surface with
  42 *     the point coordinates
  43 *     SLATE(11),SLATE(12),SLATE(13) is the gradient to the surface
  44 *
  45       NTAU = 0
  46       CBA(1) = SLATE(10)
  47       CBA(2) = SLATE(11)*DIR(1)+SLATE(12)*DIR(2)+SLATE(13)*DIR(3)
  48 *
  49       CBA(3) = 0.
  50       XLINE  = .TRUE.
  51 *
  52 **              in case of a plane
  53       IF (NC.EQ.4)              GO TO 200
  54 *
  55 *     in case it is a simplified surface X=-C0,Y=-C0,Z=-C0, or X*2+Y*2=-C0
  56 *
  57       IF (NC.EQ.2)              THEN
  58         IAX  = C(2)
  59         IF (IAX.NE.4)           GO TO 200
  60         CBA(3) = DIR(1)**2+DIR(2)**2
  61       ELSE
  62 *
  63 **              in case it is a surface with 7 or 10 coefficients
  64         CBA(3) = DIR(1)**2*C(5)+DIR(2)**2*C(6)+DIR(3)**2*C(7)
  65 *
  66 **              in case it is a surface with 10 coefficients
  67         IF (NC.EQ.10)           THEN
  68           CBA(3) = CBA(3) + C(08)*DIR(1)*DIR(2)
  69           CBA(3) = CBA(3) + C(09)*DIR(2)*DIR(3)
  70           CBA(3) = CBA(3) + C(10)*DIR(3)*DIR(1)
  71         ENDIF
  72       ENDIF
  73       XLINE = .FALSE.
  74 *
  75   200 IF (XLINE)                THEN
  76 *
  77 *     in case it is a plane (4 coefficients) or a simplified surface
  78 *
  79         IF (1.E+6*ABS(CBA(2)).LE.ABS(CBA(1)))   GO TO 999
  80         NTAU = 1
  81         TAU(1) = - CBA(1)/CBA(2)
  82       ELSE
  83 *
  84 **              in case it is a surface with 7 or 10 coefficients
  85         CALL GVPSQR (CBA, TAU, NTAU)
  86       ENDIF
  87 *
  88   999 NTAU = MAX(0,NTAU)
  89       RETURN
  90       END