def test_fresnel_coefs(self):
self.assertEqual(geo.fresnel_coefs(1.0, 0, 1.0), (0.0, 1.0))
R,T = geo.fresnel_coefs(1.6, 0.5, 1.0)
self.assertAlmostEqual(R, 0.072538667, places=6)
self.assertAlmostEqual(T, 0.927461332, places=6)
#angles which exceed TIR should return nans:
tir_angle = geo.tir_angle(1.6, 1.0)
self.assertTrue(all(numpy.isnan(geo.fresnel_coefs(1.6,
tir_angle + 0.01,
1.0))))
def refract_ray(ray, normal, ni, nt):
#TODO: docstring
#normal is a numpy array.
#assumption: normal is pointed towards ni (the incoming rays)
eta = ni / nt #ratio of indices
c1 = -numpy.dot(ray.direction, normal)
cs2 = 1 - eta**2 * (1 - c1**2)
if cs2 > 0:
#ray is transmitted
trans_ray = copy.copy(ray)
trans_ray.direction = eta * ray.direction +\
(eta * c1 - numpy.sqrt(cs2)) * normal
theta_i = -numpy.arccos(c1)
R, T = geo.fresnel_coefs(ni, theta_i, nt)
trans_ray.intensity *= T
else:
#TIR occurs in this case
R = 1.0
trans_ray = None
ray = reflect_ray(ray, normal) #note: modified in-place
ray.intensity *= R
return trans_ray, ray #transmitted, reflected
