Pixels per degree (PPD) in virtual reality are more important than resolution and pixel per inch which is connected with the field of view. The VR companies are often advertising it, e.g., Varjo XR-4 has pixels per degree 51. However, I have some questions about the measurements and some other relevant data:
How do the companies measure pixels per degree? The common approach should be to divide the horizontal resolution/ horizontal (mono) Field of View. However, this is just a naive approach and did not consider the lens distortion or viewing distance. What would be the best formula to calculate pixels per degree?
The highest pixels per degree for humans should be 60, and in that case, the highest cycles per degree (cpd) should be 30 (for 20/20 vision). That makes cpd = 0.5*ppd. I was trying to find an accurate derivation between CPD and PPD but did not find any resources. I would like if you can suggest anything that you know.
PPD should be distance-dependent, which means the distance between the eye and the display. I have an HTC Vive Pro eye, and I was trying to find the distance between the eye and the display. But could not find it. Is it possible to get this distance without disassembling the device?