GEANT321/ggeom/gingtr.F

   1 *
   2 * $Id$
   3 *
   4 * $Log$
   5 * Revision 1.1.1.1  1995/10/24 10:20:50  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 GINGTR(X,P,IYES)
  13 C.
  14 C.    ******************************************************************
  15 C.    *                                                                *
  16 C.    *                                                                *
  17 C.    *          SUBROUTINE GINGTR(X,P,IYES)                           *
  18 C.    *      Routine performes GINME type function to determine        *
  19 C.    *      whether the point X is in the GTRA shape with parameters  *
  20 C.    *      P. IYES is returned 1 if it is 0 if not.                  *
  21 C.    *          A.C.McPherson 22nd April 1985                         *
  22 C.    *                                                                *
  23 C.    *      Called by : GINME                                         *
  24 C.    *                                                                *
  25 C     ******************************************************************
  26 C.
  27       DIMENSION X(3),P(30),XPT(4),YPT(4)
  28 C.
  29 C.            ----------------------------------------
  30 C.
  31 C             First the range in Z is checked.
  32 C
  33       IYES=0
  34       IF(ABS(X(3)).GT.P(1)) GO TO 30
  35 C
  36 C             Next the four corners at the z of the input point (X(3))
  37 C             are computed as:
  38 C
  39       DO 10 I=1,4
  40       I0=I*4+11
  41       XPT(I) = P(I0)+P(I0+2)*X(3)
  42       YPT(I) = P(I0+1)+P(I0+3)*X(3)
  43    10 CONTINUE
  44 C
  45 C             Then the cross product between the vector from that
  46 C             corner to the input point and the vector from that corner
  47 C             to the next corner is computed and its sign is
  48 C             interrogated. Since the quadralateral is convex, if any
  49 C             one of these signs is wrong, the point is outside the
  50 C             shape. This task is performed as follows:
  51 C
  52       DO 20 I=1,4
  53       J = I+1
  54       IF(J.EQ.5) J=1
  55       CROSS = (X(1)-XPT(I))*(YPT(J)-YPT(I)) -
  56      +        (X(2)-YPT(I))*(XPT(J)-XPT(I))
  57       IF(CROSS.GT.0.0) GO TO 30
  58    20 CONTINUE
  59       IYES = 1
  60    30 CONTINUE
  61       RETURN
  62       END