/*******************************************************************************
*
* McStas, neutron ray-tracing package
*         Copyright 1997-2002, All rights reserved
*         Risoe National Laboratory, Roskilde, Denmark
*         Institut Laue Langevin, Grenoble, France
*
* Component: Collimator_ROC
*
* %IDENTIFICATION
*
* Written by: <a href="mailto:hansen@ill.fr">Thomas C Hansen</a>
* Date: 15 May 2000
* Version: $Revision: 1.2 $
* Origin: <a href="http://www.ill.fr">ILL</a> (Dif/<a href="http://www.ill.fr/YellowBook/D20">D20</a>)
* Release: McStas 1.6
* Modified by: J.Ollivier Nov 2001: cleaned the code
*
* Radial Oscillationg Collimator (ROC)
*
* %DESCRIPTION
*
* This is an implementation of an Ideal radial oscillating collimator,
* which is usually placed between a polycrystalline sample and a linear
* curved position sensitive detector on a 2-axis diffractometer like D20.
* The transfer function has been implemented analytically, as this is
* much more efficient than doing Monte-Caqrlo (MC) choices and to absorb
* many neutrons on the absorbing blades. The function is basically triangular
* (except for rather 'exotic' focuss apertures) and depends on the distance
* from the projection of the focus centre to the plane perpendicular to the
* collimator planes to the intersection of the same projection of the velocity
* vector of the neutron with a line that is perpendicular to it and containing
* the same projection of the focus centre. The oscillation is assumed to be
* absolutely regular and so shading each angle the same way. All neutrons not
* hitting the collimator core will be absorbed.
*
* Example: Collimator_ROC(
*     ROC_pitch=5, ROC_ri=0.15, ROC_ro=0.3, ROC_h=0.15,
*     ROC_ttmin=-25, ROC_ttmax=135, ROC_sign=-1, ROC_present=1)
*
* %PARAMETERS
*
* INPUT PARAMETERS:
*
* ROC_pitch:  [deg] Angular pitch between the absorbing blades (1)
* ROC_ri:     [m]   Inner radius of the collimator             (0.4)
* ROC_ro:     [m]   Outer radius of the collimator             (1.2)
* ROC_h:      [m]   Height of the collimator                   (0.153)
* ROC_ttmin:  [deg] Lower scattering angle limit               (0)
* ROC_ttmax:  [deg] Higher scattering angle limit              (100)
* ROC_sign:   [1]   Chirality/takeoff sign                     (1)
* ROC_present:[1]   Presence flag of this component            (1)
*
* %LINKS
* <a href="http://www.ill.fr/YellowBook/D20/McStas/d20.instr">Source code of d20.instr</a>, where this component is used
* <a href="http://www.ill.fr/YellowBook/D20/McStas/">Components for the simulation of D20</a>
*
* %END
*
*******************************************************************************/


DEFINE COMPONENT Collimator_ROC
DEFINITION PARAMETERS ()
SETTING PARAMETERS (ROC_pitch,ROC_ri,ROC_ro,ROC_h,ROC_ttmin,ROC_ttmax,ROC_sign=1,ROC_present=1)
STATE PARAMETERS (x,y,z,vx,vy,vz,t,s1,s2,p)
INITIALIZE
%{
  if (ROC_pitch <= 0 || ROC_ri > ROC_ro || ROC_ro <= 0
    || ROC_h <=0 || ROC_ttmin > ROC_ttmax)
  fprintf(stderr,"Collimator_ROC: error: %s: Invalid geometrical parameters.\n", NAME_CURRENT_COMP);
%}

TRACE
%{
  double ROC_angle,x0,z0,x1,z1,a,r,xp,zp;
  double d,dt,pi,t0,t1,t2,t3,twotheta;
  if (ROC_present)
  {
    if (cylinder_intersect(&t0, &t1, x, y, z, vx, vy, vz, ROC_ri, ROC_h) && t1 > 0)
    {
      int MyAbsorb = 0;

      if (t0 < 0) t0 = t1;
      twotheta = -atan2(x+vx*t0,z+vz*t0);
      if (( (double)ROC_sign*twotheta*RAD2DEG >= ROC_ttmin ) && ( (double)ROC_sign*twotheta*RAD2DEG <= ROC_ttmax ))
      {
        if (cylinder_intersect(&t2, &t3, x, y, z, vx, vy, vz, ROC_ro, ROC_h) && t3 >0)
        {
          dt=(x*vz-z*vx)/(vx*vx+vz*vz);
          xp=vz*dt;
          zp=-vx*dt;
          d=sqrt(xp*xp+zp*zp);
          pi=1.0-RAD2DEG*fabs(asin(d/ROC_ro)-asin(d/ROC_ri))/ROC_pitch;
          if (pi>0)
             p*=pi;
          else MyAbsorb = 1;
        }
        else MyAbsorb = 1;
      }
      else MyAbsorb = 1;
      if (MyAbsorb)
      {
        PROP_DT(t0);
        ABSORB;
      }
    }
    else ABSORB;
  }
%}
MCDISPLAY
%{
  double ROC_angle,x0,z0,x1,z1;

  if (ROC_present==1)
  {  magnify("xz");
     for (ROC_angle=ROC_ttmin; ROC_angle <= ROC_ttmax; ROC_angle += ROC_pitch)
     {
       x0=ROC_ri*sin(ROC_angle*DEG2RAD);
       z0=ROC_ri*cos(ROC_angle*DEG2RAD);
       x1=x0/ROC_ri*ROC_ro;
       z1=z0/ROC_ri*ROC_ro;
       multiline(5,
        x0,  ROC_h/2, z0,
        x0, -ROC_h/2, z0,
        x1, -ROC_h/2, z1,
        x1,  ROC_h/2, z1,
        x0,  ROC_h/2, z0);
     }
  }
%}
END
