[Gaze origin and direction issue from GetGazeRay in Unreal Plugin]

Hello,

I think there still is an issue with GetGazeRay in the Unreal SDK.

The following two posts already address this issue and there is a fix now in the version i am using (SDK-v1.3.3.0) and this fix is based on the bug fix suggested in the first post (Gaze origin bug in GetGazeRay of Unity package). This means the x-direction is just multiplied by -1:

origin.x *= -1; // Adding this line fixes the bug
direction.x *= -1;

 

Now the issue is that this fix works fine for Unity since the coordinate system is a left-handed, Y-Up coordinate system (see also: A Guide to Unity’s Coordinate System (With Practical Examples) – techarthub ). However, Unreal is a left-handed, Z-Up coordinate system. This means that the fix for Unity is not valid for Unreal which i can confirm based on my own observations.

So the fix for the direction in Unreal would simply be:

direction.Y *= -1;

 

Furthermore, for the origin of the eyes the SRanipal SDK uses a right-handed coordinate system:

in SRanipal_Eyes_Enums.h

/** The point in the eye from which the gaze ray originates in millimeters.(right-handed coordinate system)*/
FVector gaze_origin_mm;

is used in SRanipal_Core.cpp

origin = singeEyeDatas[(int)gazeIndex].gaze_origin_mm / 1000;
...
CovertToUnrealLocation(origin);

The ConvertToUnrealLocation(origin) translates the SDK coordinate system to the Unreal coordinate system but still the values along the Unreal y-axis are flipped. 

That is why i also included this:

origin.Y *= -1;

 

So my complete fix looks like this:

origin = singeEyeDatas[(int)gazeIndex].gaze_origin_mm / 1000;
direction = singeEyeDatas[(int)gazeIndex].gaze_direction_normalized;
// direction.X *= -1; is the fix for the origin bug in Unity. However, Unreal uses a different coordinate system.
// that is why line direction.X *= -1; is commented 
//direction.X *= -1;
CovertToUnrealLocation(origin);
ApplyUnrealWorldToMeterScale(origin);
CovertToUnrealLocation(direction);
origin.Y *= -1;
direction.Y *= -1;

 

Please, just tell me if that is correct or if i am missing something here... (or i am just repeating a post i did not find 🙂 )

Thank you!