void PHG4HoughTransform::projectToRadius(const SvtxTrack& track, double radius, vector<double>& intersection)
{
float phi = track.phi;
float d = track.d;
float k = track.kappa;
float z0 = track.z0;
float dzdl = track.dzdl;
intersection.clear();intersection.assign(3,0.);
double& x = intersection[0];
double& y = intersection[1];
double& z = intersection[2];
float rad_det = radius;
float cosphi = cos(phi);
float sinphi = sin(phi);
// get outer hit
float hitx = d*cosphi;
float hity = d*sinphi;
int nhits = track.getNhits();
for(int l=(nhits-1);l>=0;l-=1)
{
if(track.getClusterID(l) >= 0)
{
hitx = track.getHitPosition(l, 0);
hity = track.getHitPosition(l, 1);
break;
}
}
k = fabs(k);
float kd = (d*k + 1.);
float kcx = kd*cosphi;
float kcy = kd*sinphi;
float kd_inv = 1./kd;
float R2 = rad_det*rad_det;
float a = 0.5*(k*R2 + ( d*d*k + 2.*d ))*kd_inv;
float tmp1 = a*kd_inv;
float P2x = kcx*tmp1;
float P2y = kcy*tmp1;
float h = sqrt(R2 - a*a);
float ux = -kcy*kd_inv;
float uy = kcx*kd_inv;
float x1 = P2x + ux*h;
float y1 = P2y + uy*h;
float x2 = P2x - ux*h;
float y2 = P2y - uy*h;
float diff1 = (x1-hitx)*(x1-hitx) + (y1-hity)*(y1-hity);
float diff2 = (x2-hitx)*(x2-hitx) + (y2-hity)*(y2-hity);
float signk = 0.;
if(diff1 < diff2){signk = 1.;}
else{signk = -1.;}
x = P2x + signk*ux*h;
y = P2y + signk*uy*h;
double sign_dzdl = sign(dzdl);
double startx = d*cosphi;
double starty = d*sinphi;
double D = sqrt((startx-x)*(startx-x) + (starty-y)*(starty-y));
double v = 0.5*k*D;
z = 0.;
if(v > 0.1)
{
if(v >= 0.999999){v=0.999999;}
double s = 2.*asin(v)/k;
double dz = sqrt(s*s*dzdl*dzdl/(1. - dzdl*dzdl));
z = z0 + sign_dzdl*dz;
}
else
{
double s = 0.;
double temp1 = k*D*0.5;temp1*=temp1;
double temp2 = D*0.5;
s += 2.*temp2;
temp2*=temp1;
s += temp2/3.;
temp2*=temp1;
s += (3./20.)*temp2;
temp2*=temp1;
s += (5./56.)*temp2;
double dz = sqrt(s*s*dzdl*dzdl/(1. - dzdl*dzdl));
z = z0 + sign_dzdl*dz;
}
}
