The goal is to calculate and visualize the solid angle of a cylindric detector seen from a gaussian source.
Afterwards, we also want to calculate the interaction probabilities depending on the material of the cylinder.

The "program" is made of two parts:
1)tirMGauss->Generates isotropic rays from a gaussian source and saves those that intersect with the cylinder in a textfile.
2)display_3D->Reads the previous file and creates a 3D display. It also generates a copy of the read data and an "intersections.txt" file which contains the coordinates of the intersections.

Syntax:

void tirMGauss(
	char *filename, //name of the file where the ray data is stored
	int N=20000, //number of rays generated (different from the number of intersecting rays)
	double sigma=1, //RMS of the gaussian source
	double xd=5, //x position of the cylinder (center of the bottom of the cylinder)
	double yd=0, //y position of the cylinder (center of the bottom of the cylinder)
	double zd=10, //z position of the cylinder (center of the bottom of the cylinder)
	double dl=8, //height of the cylinder
	double r0=2) //radius of the cylinder

void display_3D(
	char* filename, //name of the file where the ray data is stored
	int Nppl=200, //nb of points/line for the 3D lines
	bool disp_cyl=true, //display the cylinder
	bool disp_main_base=true, //display the main base (placed so that z(cylindre)=0)
	bool disp_source_base=true, //display the source base
	bool disp_rays=true, //display the rays (=0,1,2,3)(yellow=intersects, green=does not intersect)
	bool disp_in_pts=true, //display entry points
	bool disp_out_pts=true, //display exit points
	bool disp_src_pts=true) //display source points

Note:
-disp_rays=0: no rays displayed
-disp_rays=1: rays stop at entry points
-disp_rays=2: rays stop at exit points
-disp_rays=3: rays have a fixed length (2*range)