\begin{tikzpicture}[scale=1.25]

% Constants

	% Sphere radius
	\def\r{2}

% Clip region

	%\tkzInit
	\tkzInit[xmin=-1.0,xmax=4.5,ymin=-0.5,ymax=2.1]
	\tkzClip

% Points

	% Special points

		% Origin (viewpoint)
		\tkzPoint*(0,0){O}

		% Sphere center
		\tkzPoint*(4,0){C}

		% Ground position
		\tkzPoint*(2,0){G}

	% Intersections

		% Direction point for ray
		\tkzPoint*(1,0.55){Odr}

		% Intersect tangent ray with maximum sphere
		\tkzInterLCR(Odr,O)(C,\r cm){P}{U}

	% Unit vectors

		% Calculate ray vector
		\tkyUnitVect(O,Odr){r}

	% Create vectorpoints

		% Ray at O
		\tkyPointVectL(O,r,0.5){Ovr}

% Drawing

	% Points

		% Origin
		\tkzDrawPoint[pos=below left](O)

		% Sphere center
		\tkzDrawPoint[pos=below right](C)

		% Intersection position
		\tkzDrawPoint[pos=above left](P)
		
		% Ground point
		\tkzDrawPoint[noname](G)

	% Line segments

		% From O to C
		\tkzSegment[style=solid,label=$a$,poslabel=-16pt,time=0.5](O/G)
		\tkzSegment[style=solid](G/C)

		% Ray dashed line
		\tkzSegment[style=solid,label=$t$,poslabel=0pt,time=0.5](Ovr/P)

		% From C to P
		\tkzSegment[style=solid](C/P)

		% From P to G
		\tkzSegment[style=solid](P/G)

	% Vectors

		% Ray at O
		\tkzDrawVector(O/Ovr);
		\tkzDrawPoint[name=\unit{r},pos=above left,size=0](Ovr)

	% Sphere
	
		\tkzCircleR[lw=1pt](C,\r)

	% Angles

		% Ray angle
		\tkzMarkAngle[size=0.45,dist=0.12,labelsize={},label={\omega}](P/O/C)

		% Normal angle
		\tkzMarkAngle[size=0.45,dist=0.12,labelsize={},label={\gamma}](P/C/O)

		% Isosceles
		\tkzMarkAngle[style=aii,size=0.25,dist=0.12,labelsize={},label={}](C/P/G)
		\tkzMarkAngle[style=aii,size=0.25,dist=0.12,labelsize={},label={}](C/G/P)

		% Chi
		\tkzMarkAngle[size=0.55,dist=0.15,labelsize={},label={\chi}](O/P/G)

		% Rho
		\tkzMarkAngle[size=0.25,dist=0.07,labelsize={},label={\rho}](O/G/P)

\end{tikzpicture}
