\begin{tikzpicture}[scale=1.25]

% Constants

	% Sphere radius
	\def\r{18}

% Clip region

	\tkzInit[xmin=-1,xmax=4,ymin=0.5,ymax=3]
	\tkzClip

% Points

	% Sphere center
	\tkzPoint*(0,-17){C}

	% Frustum
	\tkzPoint*( 0,2){F0}
	\tkzPoint*(10,5.4){F1}
	\tkzPoint*(10,-2.10){F2}

	% Bottom frustum intersection
	\tkzInterLCR(F2,F0)(C,\r cm){I2}{O2}

	% Vector points
	\tkzPoint*(0,1.5){F0v}
	\tkzPoint*(0,1.0){F0v2}
	%\tkzVectorNormalised(F0,C){F0v}

% Drawing

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

	% Frustum
	\tkzSegment(F0/F1)
	\tkzSegment(F0/I2)
	\tkzSegment[style=dashed](F0v/F0v2)

	% Vectors
	\tkzDrawVector(F0/F0v)
	\tkzDrawPoint[name=$\unit{n}$,pos=above left,size=0](F0v)
	\tkzDrawPoint[name=I,pos=above](I2)

	% Arc
	\tkzArcR[color=blue,lw=2pt](C,\r)(90,80.2)

	% Curvy terrain
	\draw [color=blue] (0,0.5) .. controls (1,1.5) and (2,1.2) .. (3.1,0.195);

\end{tikzpicture}
