montecarlo.cpp 1.73 KB
``````#include "montecarlo.h"
#include "rts/math/quaternion.h"
#include "rts/math/matrix.h"
#include <iostream>
#include <stdlib.h>
using namespace std;

void mcSampleNA(bsVector* samples, int N, bsVector k, ptype NAin, ptype NAout)
{
/*Create Monte-Carlo samples of a cassegrain objective by performing uniform sampling
of a sphere and projecting these samples onto an inscribed sphere.

samples = rtsPointer to sample vectors specified as normalized cartesian coordinates
N       = number of samples
kSph	= incident light direction in spherical coordinates
NAin    = internal obscuration NA
NAout   = outer cassegrain NA
*/

//get the axis of rotation for transforming (0, 0, 1) to k
//k = -k;
ptype cos_angle = k.dot(bsVector(0, 0, 1));
rts::matrix<ptype, 3> rotation;
if(cos_angle != 1.0)
{
bsVector axis = bsVector(0, 0, 1).cross(k).norm();

ptype angle = acos(cos_angle);
rts::quaternion<ptype> quat;
quat.CreateRotation(angle, axis);
rotation = quat.toMatrix3();
}

//find the phi values associated with the cassegrain ring
ptype inPhi = asin(NAin);
ptype outPhi = asin(NAout);

//calculate the z-values associated with these angles
ptype inZ = cos(inPhi);
ptype outZ = cos(outPhi);

ptype rangeZ = inZ - outZ;

//draw a distribution of random phi, z values
ptype z, phi, theta;
for(int i=0; i<N; i++)
{
z = ((ptype)rand() / (ptype)RAND_MAX) * rangeZ + outZ;
theta = ((ptype)rand() / (ptype)RAND_MAX) * 2 * (ptype)PI;

//calculate theta
phi = acos(z);

//compute and store cartesian coordinates
bsVector spherical(1, theta, phi);
bsVector cart = spherical.sph2cart();
samples[i] = rotation * cart;
}

}``````