Asking for the a_ratio & b_ratio

[zxcheergo]

Thanks for your wonderful project! I am curious about how to convert the physical size to the screen size. I noticed that you used some special ratio and the PPI should not be the same as iPhone XR. So could please provide more details about how you calculate these parameters? Thank you in advance !

[Shiru99]

Pls refer this:

• eye-tracking-ios-prototype by virakri for the calculation of screenX and screenY.

[zxcheergo]

Thanks for your reply! I have a further question. I noticed that you deal with the screenX with the following code:

let screenX = transformedLookAtPoint.y / (Float(Device.screenSize.width) / 2) * Float(Device.frameSize.width)
Why the screenX is calculated from the lookAtPoint.y?

Plus, what's the origin of screenX and LookAtPoint in their corresponding coordinate? Why you use the half of the screenSize.width?

[Shiru99]

Since the camera location is in the center of the screen (in portrait orientation), while considering width we need to consider only half of the width

For other questions, once I get free I will go through the code and add answers here soon

[zxcheergo]

Thanks for your reply! About half of the width, can I assume that the origin of camera coordinate should be at the camera? And the screen coordinate system's origin should be at the top left corner of the screen? Following this assumption, If we divide half of the screen width, should we also multiply half of the width of the framesize? Afterwards, we can compensate the screenX by adding the points from the origin of screen coordinate system to the camera? I tried to draw an illustration for this.
I think we could calculate the screenX from the following equation:
screenX = Fix Point X / (screen size width / 2) * (frame size width / 2) + compensation

[sosoyososo]

Pls refer this:

• eye-tracking-ios-prototype by virakri for the calculation of screenX and screenY.

Thanks for your code and post https://shiru99.medium.com/eye-tracking-with-arkit-ios-part-ii-2723f9bfe04e .

After read both of your code, I added my cal method here. Do I make a right calculation ?
virakri/eye-tracking-ios-prototype#3