Calculate aspect ratio from 2D shape in 3D space
The ratio is with a quick and dirty visual measurement $665:501$ which is approximately $5:4$. You can measure it by taking the ratio of the vanishing angles $\alpha/\beta$ (see picture 1) because we are so close to the center.



Image 1: Ratio of the inbound angles

We can check the situation visually by drawing a 2 point perspective grid. For this we need the center line between the vanishing points.



Image 2: Seems about right.