Prueba a mover el vértice libre hasta intersecar dos lados.

POLÍGONO CRUZADO (los que no usaremos)

POLÍGONO SIMPLE (los que usaremos)

A = (2.8199999999999976, 3.16)
B = (2.3199999999999976, 0.32)
C = (4.979999999999998, 2.5)
D = (2.3199999999999976, 4.98)
poly1, a, b, c, d = Polygon(A, B, C, D)
E = Intersect(a, c)
F = Intersect(b, d)
G = (-3.2800000000000025, 3.92)