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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