Projection Matrices

Project Matrix

The projection of $\left(\frac{fx}{z},\frac{fy}{z}\right)$ is matrix multiplication.

$$\left[\begin{array}{c}fx\\ fy\\ z\end{array}\right]\equiv \left[\begin{array}{cccc}f& 0& 0& 0\\ 0& f& 0& 0\\ 0& 0& 1& 0\end{array}\right]\left[\begin{array}{c}x\\ y\\ z\\ 1\end{array}\right]\to \left[\begin{array}{c}\frac{fx}{z}\\ \frac{fy}{z}\end{array}\right]$$

Why $\equiv$ and not $=$