Above is a 3D representation of the given point A(3,2,-5). The point is below the x-y grid. B(3,2,0) and C(0,2-5) are projections of A on to x-y and y-z planes respectively.
Below is Monge's projection with the two planes. In effect, the x-y plane is folded up along the y-axis into the y-z plane to form a 2D representation of A. In this representation the projections of A are shown as B(x=3,y=2) and C(y=2,z=-5). The upper vertical half-axis OX (red) represents the x-axis in the 3D representation; the lower vertical half-axis OZ (blue) represents the z-axis in the 3D representation. The horizontal y-axis and OY (green) is common in both representations.
