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CAngle.cpp
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CAngle.cpp
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#include "CAngle.h"
using namespace std;
// following line is needed in ROOT version
//ClassImp(CAngle)
float const CAngle::pi=acos(-1.);
/**
* Constructor
*/
CAngle::CAngle(float theta0, float phi0)
{
theta = theta0;
phi = phi0;
}
//************************************************
CAngle CAngle::transform(CAngle angle1, CAngle angle2)
/**
* This subroutine performs a rotational transformation.
*
* theta1,phi1 are the coordinates (spherical angles in
* radians)of a unit vector in the original coordinate systems.
* the z axis is made to rotate in the phi=phi2 plane by an
*angle theta2. The coordinates of the vector in the new
*reference frame are theta3,phi3
\param angle1 is the initial (theta,phi) angles
\param angle2 specifies the (theta,phi) rotation
*/
{
//
// To calculate the angle between two vectors
// theta1,phi1 and theta2,phi2
// use CALL transform(theta1,phi1,-theta2,phi2,theta3,phi3)
// i.e. theta3 in the angle between them, note the negative sign
// on theta2
// rotate vector in x-y plane by -phi2
// and find cartesian coordinates
float xp = sin(angle1.theta)*cos(angle1.phi-angle2.phi);
float yp = sin(angle1.theta)*sin(angle1.phi-angle2.phi);
float zp = cos(angle1.theta);
// rotate vector in z-x plane by theta2
float zt = zp*cos(angle2.theta) - xp*sin(angle2.theta);
float xt = xp*cos(angle2.theta) + zp*sin(angle2.theta);
float yt = yp;
// rotate vector in x-y plane back by +phi2
// and find spherical coordinates
float theta3, phi3;
if (xt == 0.0 && yt == 0.0) phi3 = 0.;
else
{
phi3 = atan2(yt,xt) + angle2.phi;
if (phi3 >2.* pi) phi3 = phi3 - 2.*pi;
if (phi3 < 0.0) phi3 = phi3 + 2.*pi;
}
if (zt > 1.0) theta3 = 0.;
else if (zt < -1.0) theta3 = pi;
else theta3 = acos(zt);
CAngle angle3(theta3,phi3);
return angle3;
}

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