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import numpy as np
def beam2FaceDistance(beam, face):
# return distance to face if beam hits it or infinity otherwise
# for beams and faces structure description see face_beam_interaction.m
# default return values for the case when beam misses the face
isFaceHit = False
hitPosition = [float('NaN'), float('NaN')]
hitDistance = float('Inf')
k = beam.k
# face direction or kf
kf = face.vertex2 - face.vertex1 # not a unit vector
# simple check for intersection of two vectors
# if beam are parallel no intersection is possible
# we do this via cross product calculation
angleTolerance = 1e-14;
if abs(np.cross(k, kf)) <= angleTolerance:
# beams misses face
return [hitDistance, hitPosition, isFaceHit]
# let's find the intersection of lines passing through face and light beam
# we introduce parameters tb and tf
# which define distance (in arb. units) along k vectors
# we are solving
# xb_o+ k_x*tb = v1_x+ kf_x*tf
# yb_o+ k_y*tb = v1_y+ kf_y*tf
# A*t = B
A = np.array([[k[0], -kf[0]],\
[k[1], -kf[1]]])
B = np.array([[face.vertex1[0] - beam.origin[0]],\
[face.vertex1[1] - beam.origin[1]]])
A = np.linalg.inv(A)
t = np.dot(A, B)
tb = t[0]
tf = t[1]
# beam intersects face only if 0<=tf<=1 and tb>=0
if 0 <= tf and tf <= 1 and tb >= angleTolerance:
# intersection, beam hits the face
isFaceHit = True
else:
# beam misses the face
return [hitDistance, hitPosition, isFaceHit]
# calculating hit position
hitPosition = face.vertex1 + kf * tf
hitDistance = tb # distance along the light beam
return [hitDistance, hitPosition, isFaceHit]
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