An object $X$ is viewed from a camera placed at point $C_{1}$. The camera is then moved to the point $C_{2}$ and $X$ is again viewed from this new position. Suppose $H$ is the plane containing the points $C_{1}$ and $C_{2}$. Let $H^{\prime}$ be a plane parallel to $H$ lying between the object $X$ and the camera positions. Let $f$ denote the distance between $H$ and $H^{\prime}$. Let $X_{1}, X_{2}$ be the points of intersection of $H^{\prime}$ with the line segments joining $X$ with $C_{1}$ and $C_{2}$ respectively.
Let $x_{1}$ be the distance between the reference axis $L_{1}$ and $X_{1}$. Similarly let $x_{2}$ be the distance between the reference axis $L_{2}$ and $X_{2}$. The axes $L_{1}$ and $L_{2}$ are both perpendicular to the camera plane $H$. The difference $\left|x_{1}-x_{2}\right|$ is called the disparity in views. Find a formula for the depth $z$ i.e. distance of the object from the camera plane in terms of $f$, the distance $b$ between the cameras, and the disparity.
