>>5883343What is there not to get?
He is using a floor plan to draw a perfect cube. Floor plans are completely flat, and so are are the sides of the square at the station point and that lie on the edges or vanishing lines that form the 90 degree cone of vision. This is because when you stand on one corner of a square and look down on the sides and edges closes to you, it is still mostly square and not distorted by perspective. Normally, you shouldn't be able to see your feet when looking off into the distance, so this is not realistic. But he is using this to explain a concept.
The height of the cube is the same length as the two sides at the edge of 90 degrees cone of vision. This is because that corner of the cube also lies on the edges of the 90 degree cone of vision. The concept being pushed is that lines on the edges of 90 degree cone of vision are flat and not distorted by perspective.
But the other two sides of the square that are not on the edges of the 90 degree cone of vision will be distorted by perspective. Therefore we need a way to put those other sides in perspective. To do that, he just used the floor plan method. Then you connect the rest of the cube using 3 vanish points as he demonstrates in the last panel.
