ECE532 Biomedical Optics
©1998
Steven L. Jacques, Scott A. Prahl
Oregon Graduate Institute
to next page

Chapter 4
Course
Home

Time-resolved Monte Carlo:

Launch photons.

The first step is to launch a photon. In this example implementation, the photons are launched as an isotropic point source in 3 dimensions bookkeeped using Cartesian coordinates.

/**** LAUNCH 
*   Initialize photon position and trajectory.
*   Implements an isotropic point source.
*****/
i_photon += 1;	            /* increment photon count */

photon_status = ALIVE;      /* Launch an ALIVE photon */
L = 0;                      /* set photon's accumulated pathlength to zero */
it = 0;                     /* set pointer to timepoint T[1] */

x = 0;                      /* Set photon position to origin. */
y = 0;
z = 0;

/* Randomly set photon trajectory to yield an isotropic source. */
costheta = 2.0*RandomNum - 1.0;   
sintheta = sqrt(1.0 - costheta*costheta);	/* sintheta is always positive */
psi = 2.0*PI*RandomNum;
ux = sintheta*cos(psi);
uy = sintheta*sin(psi);
uz = costheta;

to next page | Chapter 4 | Course | Home