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Coordinate of gaze origin and direction


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Dear HTC support team,

I'm writing this post to ask you to confirm the coordinate of gaze origin and direction.

According to the following manual, the coordinate system is based on right-handed.

image.png.b43d51b8eb823627ef04576f04a2baa2.png

 

I checked the recorded data, follwoing the coordinate system, but it looks that the measured values are inverse, though my understanding might be wrong. For example, the follwoing data show the gaze origin and direction of right eye. As you can see, the gaze orign on z axis has negative value and that on x axis also has negative value. If we follow the right-handed coordinate system, these values should be positive, shouldn't they?

image.png.7aafecaeb73db8c58a33eafc5f7d2c52.png

image.png.cc93ce117f5230ddf8204d3344334d91.png

 

In addition, it seems that the value of gaze direction is also invert. For instance, the following first picture shows the change of gaze direction on X axis when I move my eye to the right side. As shown in the figure, the value changes to negative direction, whereas the next figure of pupil position changes to positive direction.

image.png.0b9022529f3aafc3efbe2ac6f7fad83e.png

image.png.b0ec0769ee74475bcdd2e19da3fde91d.png

 

It is appreciated if you can confirm the configuration of coordinate system. I'm sorry if my understanding is wrong.

Thank you very much for your support.

 

Best regards,

imarin18

@Corvus @Daniel_Y

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Dear HTC support team,

I think I figured out the configuration of coordinate system. I was observing the values, assuming that the origin of coordinate was on eyes. However, I guess that the origin of coordinate is on the VR headset. If that being the case, the positive/negative sign of the measured data makes sense.

In addition, I think that the configuration of pupil position will be as follows: (0,0) on the bottom left corner of the lens and (1,1) on the top right corner of the lens from the perspectives of eyes, not the direction from the VR headset.

Could you please confirm whether the understanding is correct?

Best regards,

imarin18

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Dear HTC support team,

According to my investigation, it does not seem that the gaze direction data are normalised between 0 and 1 as described in the manual. I reckon the data are in the range of [-pi/2 pi/2], though I am not sure if my understanding is correct. Could you please confirm the data configuration?

Best regards,

imarin18

 

@Daniel_Y @Corvus

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  • The coordinate system is with respect to the system origin as the figure below.
  • "normalized" means x, y, z of gaze vector is in the 0~1, i.e. a unit vector in Cartesian coordinate.
  • Regarding the normalized pupil position, (0, 0) is the top left of sensor area and (1, 1): is the bottom right of sensor area,

 

 

Gaze.png

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On 2/25/2020 at 1:37 AM, Somnath said:

Can you please explain how are you exactly finding the gaze point from gaze origin and gaze direction as gaze direction is normalized vector. Do we need to unnormalize it, if yes then how shall i do this ?

Are u using Unity? If so, you could take a look at EyeFocusSample enclosed in Unity Plugin

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Dear @Daniel_Y

Thank you very much for your reply and the information.

According to the data from my measurement, the gaze direction data are not in the range between 0 and 1 as shown in the figure below. The data even have negative values. In my measurement, I intentionally moved my eyes at +/-8 degrees from the central point. Assuming that the data were normalised between -pi/2 and pi/2, I calculated the degrees and found the subsequent figure, showing that my eyes moved to +/-8 degrees as expected.

I'm sorry to ask you again and I may be still wrong, but could you please double confirm the configuration?

 

Normalised data in my measurement.

image.png.44c09eac15483f59f1bbefada265aa99.png

 

Data in degrees assuming that the normalised data are between -pi/2 and pi/2.

image.png.d9c70e90db5ac327005069e25fe4a9d2.png

 

 

As for the normalised pupil position, do you mean the position from the direction of the VR headset?

 

Thank you very much for your support and the information you could provide.

Best regards,

imarin18

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  • 2 weeks later...

Dear @Daniel_Y

 

Thank you very much for your reply and the information. First of all, I made a wrong description in my previous post. I was supposed to write "Data in degrees assuming that the normalised data are between -pi and pi.", not "Data in degrees assuming that the normalised data are between -pi/2 and pi/2."

 

Could you please explain how the device normalises the gaze direction data? For example, what is the situation when the gaze direction on x-axis is 1?

According to the technical specification, the trackable field of view of this headset is 110 degrees. I reckon that -1 of the gaze direction data means -55 degrees and 1 means 55 degrees. Is my understanding correct?

I check the pupil position as well. Could you please explain the configuration of pupil position as well? Does 0 mean -55 degrees and 1 mean 55 degrees?

 

Thank you very much for the information you could provide.

 

Best regards,

imarin18

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Dear @Daniel_Y

I think I figured out the calculation of angle in degrees. We simply need to follow the concept of trigonometric functions, don't we? For example, if we want to calculate the angle of our eye movements in X direction, we just need to get the arc tangent from the data in X and Z directions.

Could you please explain what 0 and 1 mean in the normalised pupil position in terms of angle in degrees?

Best regards,

imarin18

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