Transcription: These blue lines are actually the envelope and this is what defines the circumference of the tunnel. In other words, we could have a bulge in an area or a narrow section if we wanted. In this case, most of our tunnel is pretty much the same diameter around except for perhaps the openings where you see they flare out just a little bit and we wanted it that way so that when the camera actually enters the mouth of the tunnel it has kind of a opening or a rounded appearance.
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