math - Calculating rectangle 3D coordinate with coordinate its shadow?

Question

Sometimes was a problem what is the rectangle 3D rotated and be perspective transition (for example in CSS) draw as the tetragon. But we want obtain the rectangle (width, length, Euler angle, perspective) transformed via rotate and perspective draw as the tetragon.

Answer 1

figure fig.1 points a,c diagonal rectangle(yellow) points A,C diagonal tetragon(shadow) (red)

fig.2 a,b,c,d rectangle points(yellow) A,B,C,D shadow(tetragon) (red)