Sampling rate of Tobii Eye Tracker 5 is abnormal

[Fulin]

Why is my device sampling at 33 Hz instead of 133 Hz.

[Grant [Tobii]]

Hi @liufulin, thanks for your query. The Tobii Eye Tracker 5 illuminator operates at a frequency of 33Hz whilst the image sampling rate (which determines how quickly gaze data can be captured) runs at 133Hz

Further specifications can be found @ https://help.tobii.com/hc/en-us/articles/360012483818-Specifications-for-Eye-Tracker-5

Please do let us know if you have any further queries. Best Wishes.

[Fulin]

Using the same program, I can get 90 gaze points per second with Tobii Eye Tracker 4C , but only 33 with Tobii Eye Tracker 5.

[Grant [Tobii]]

Hi @liufulin, could you kindly share the code (or program) you are using to extract this info and I will try to reproduce and see if perhaps there is an issue in the API. Thank you.

[Fulin]

code

using System;
namespace CSharpSampleStreams
{
class Program
{
static void Main(string[] args)
{
// create the interaction library
Tobii.InteractionLib.IInteractionLib intlib =
Tobii.InteractionLib.InteractionLibFactory.CreateInteractionLib(
Tobii.InteractionLib.FieldOfUse.Interactive);
// assume single screen with size 2560×1440 and use full screen (not window local) coordinates
const float width = 2560.0f;
const float height = 1440.0f;
const float offset = 0.0f;

intlib.CoordinateTransformAddOrUpdateDisplayArea(width, height);
intlib.CoordinateTransformSetOriginOffset(offset, offset);
// subscribe to gaze point data; print data to console when called
intlib.GazePointDataEvent += evt =>
{
Console.WriteLine(
“x: ” + evt.x
+ “, y: ” + evt.y
+ “, validity: ” + (evt.validity == Tobii.InteractionLib.Validity.Valid ? “valid” : “invalid”)
+ “, timestamp: ” + evt.timestamp_us + ” us”
);
};
Console.WriteLine(“Starting interaction library update loop.”);
// setup and maintain device connection, wait for device data between events and
// update interaction library to trigger all callbacks, stop after 200 cycles
const int max_cycles = 2000;
var cycle = 0;
while (cycle++ < max_cycles)
{
intlib.WaitAndUpdate();
}
// cleanup – here done explicitly with Dispose(). The alternative is to use a using statement,
// which implicitly disposes an instance when the scope is left.
intlib.Dispose();
}
}
}

[Grant [Tobii]]

Hi @liufulin, this code only shows the gaze data with the appropriate timestamp and does not display any information about sampling rate, so perhaps you meant to share something else or you are using this code indirectly to make the calculation? Thank you for the clarification.

[Hongbin Zou]

Huh, the data rate issue I asked months ago is now raised again:

Tobii 5 – ONLY 33Hz for sampling frequency?

Fulin is right. Using the same code snippet, I can also get 90 gaze points per second with Tobii Eye Tracker 4C, while 33 with Tobii Eye Tracker 5. Note that Fulin’s code actually contains information about sampling rate. Collect 2000 data points and using the first and the last timestamps, we can calculate the time interval, then the sampling rate.

And this sampling rate is almost the same as the “output_frequency” param retrieved using the Stream Engine API, that is 33hz for ET5 / 90hz for 4c.
In c# I am using the “Interop.tobii_get_output_frequency(deviceHandle, out SamplingFrequency)” function.

[Grant [Tobii]]

Hi @liufulin, @dragonus, we have now updated our 4C ET5 comparison page no to more fully demonstrate the difference in tracking styles between the two models.

Whilst the 4C has a higher raw gaze frequency, the ET5 has a higher image sampling rate providing a smoother more reliable eye-tracking experience, so it is important to understand the distinction. Our apologies for any confusion caused.

[Hongbin Zou]

Hi Grant, I noticed the comparison page have a Chinese version:
https://help.tobii.com/hc/zh-cn/articles/360008539058-Tobii-%E7%9C%BC%E5%8A%A8%E4%BB%AA4C%E5%92%8C5%E4%B9%8B%E9%97%B4%E6%9C%89%E4%BB%80%E4%B9%88%E5%8C%BA%E5%88%AB-

Could you please update the Chinese version too? Thanks.

[Grant [Tobii]]

Thanks for spotting this Hongbin, will contact the appropriate team for this. Best Wishes.

[Author]

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