\begin{tikzpicture}[scale=1.00]

% Constants

	\def\r{2.5cm} % Radius

% Define the clip region

	\tkzInit[xmin=-5.5,xmax=1.5,ymin=-0.5,ymax=3]
	\tkzClip

% Define points

	\path (-5.0, 0.0) coordinate (O)  % Viewpoint and ray origin
		  (-4.0, 0.4) coordinate (P)  % The ray goes through this point
		  ( 0.0, 0.0) coordinate (C); % Sphere center

% Intersect ray with sphere

	\tkzInterLCR(O,P)(C,\r){I_1}{I_2}

% Calculate vector points

	%\tkzVectorNormalised(O,P){Ov}
	%\tkzVectorNormalised(C,O){Cv} % Nadir
	%\tkzVectorNormalised(O,C){Ov2} % Nadir

	%% Sphere normal
	%\tkzGetVectxy(C,I){v} % Get the vector from C to I into (\vx,\vy)
	%\tkzGetPointxy(I){p} % Get the point int (\px,\py)
	%\pgfmathparse{\px + \vx}\let\rx\pgfmathresult % Add vector to I
	%\pgfmathparse{\py + \vy}\let\ry\pgfmathresult
	%\path (\rx, \ry) coordinate (Iv2);
	%\tkzVectorNormalised(I,Iv2){Iv}

% Draw points

	\tkzDrawPoint[pos=below left](O)
	\tkzDrawPoint[pos=below right](C)
	\tkzDrawPoint[pos=above left](I_1)
	\tkzDrawPoint[pos=above right](I_2)

% Draw angles

	\tkzMarkAngle[dist=0.25,labelsize={},label={\omega}](I_1/O/C)
	\tkzMarkAngle[dist=0.22,labelsize={},label={\gamma_1},size=0.85cm](I_1/C/O)
	\tkzMarkAngle[dist=0.17,labelsize={},label={\gamma_2},size=0.65cm](I_2/C/O)

	\tkzMarkAngle[dist=0.11,labelsize={},label={\epsilon_1},size=0.3cm](O/I_1/C)
	\tkzMarkAngle[dist=0.14,labelsize={},label={\epsilon_2},size=0.5cm](O/I_2/C)

% Draw vectors

	%\tkzDrawVector(O/Ov)
	%\tkzDrawVector(O/Ov2)
	%\tkzDrawVector(C/Cv)
	%\tkzDrawVector(I/Iv)

	% Vector labels
	%\tkzDrawPoint[name=$\unit{r}$,pos=above left,size=0](Ov)
	%\tkzDrawPoint[name=$\unit{n}$,pos=below,size=0](Ov2)
	%\tkzDrawPoint[name=$\unit{a}$,pos=below,size=0](Cv)
	%\tkzDrawPoint[name=$\unit{s}$,pos=above,size=0](Iv)

% Draw dashed lines

	%\tkzSegment[style=dashed](Ov/I)
	\tkzSegment[style=dashed](O/I_2)
	%\tkzSegment[style=dashed,label=$d$,poslabel=-18pt,time=0.6](Cv/Ov2)
	\tkzSegment[style=dashed,label=$d$,poslabel=-14pt,time=0.55](C/O)
	\tkzSegment[style=dashed](C/I_1)
	\tkzSegment[style=dashed,label=$r$,poslabel=-13pt](C/I_2)

	%\tkzSegmentMark[label=$d$,poslabel=-18pt,time=0.2](Cv/Ov2)

% Draw sphere

	\tkzCircleR(C,\r)

\end{tikzpicture}
