I have a basic grasp of matrices and I was just wondering to which transformation does this matrix correspond? $$A = \begin{bmatrix}x_1 & y_1 & 1 \\ x_2 & y_2 & 1 \\ x_3 & y_3 & 1\end{bmatrix}$$
It is used for calculating the area of a triangle with three known vertices as, $Area= \frac{1}{2}\det{A}$. Why are we transforming each basis vector to the $z=1$ plane?