To compute how light travels using this concept, every involved component has to be calibrated. In the next part I will explain how we approached that task then followed by the gaze tracking approach.
Regarding the lenses we wanted to maintain compatibility to the Oculus DK1 so we are using their lenses. Unfortunately, the precise lens parameters are kept secret by Oculus VR. Especially the precise shape and material parameters, particularly the index of refraction, which is a wavelength-dependent physical property and important if you want to simulate light refracting through materials in ray tracing. Additionally we have to locate the lens relative to the HMD body case which is our reference.
We had to reconstruct the precise lens shape by ourselves and used a structure-from-motion approach and curve fitting for that. We also needed the index of refraction and derived the corresponding curve using calibrated cameras with light of specific wavelengths. Finally we had to calibrate the mirrors and the cameras in the HMD and used small-scale checkerboards for that. The location of the lenses relative to the HMD body case is estimated later in the user calibration.