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SRanipal eye tracking does not reach 120 Hz sampling frequency


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Hi everyone,

I'm struggling with reaching the specified sampling rate of 120 Hz (8.33 ms) on a VIVE Pro Eye HMD.
We use the SRanipal eye callback:

SRanipal_Eye_v2.WrapperRegisterEyeDataCallback()

in a script, derived from MonoBehaviour. The registered callback is only called every 14~16 ms, which leads to approx. 62 Hz. Way below the targeted 120 Hz.

I think the PC specs are quite decent and should allow for 120 Hz sampling:

  • Windows 10Pro
  • Intel i7-10750H (specs can be found here)
  • 32GB Ram
  • GeForce RTX 2070 with Max-Q Design

Following tool versions are used:

  • SRanipal SDK & Runtime 1.3.1.1
  • Unity 2019.4.18f1

Pleas note that I am aware of these threads and articles, but did not find a explanation/solution that fits for me:
Getting VerboseData at the fastest rate possible. - Vive Eye Tracking SDK - Community Forum
Assessing Saccadic Eye Movements With Head-Mounted Display Virtual Reality Technology (nih.gov)

Already many thanks,
Scot

 

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Thanks for the answer @Corvus.
Here's a code snippet, really basic. Note that I also checked without writing to the csv file in the callback method. Instead, I simply increased a counter in the callback method and logged the time at every 120th call.

using System.Collections;
using System.Runtime.InteropServices;
using UnityEngine;
using UnityEngine.Rendering.HighDefinition;
using UnityEngine.XR;
using System;
using System.IO;
using ViveSR.anipal.Eye;
using ViveSR.anipal;
using ViveSR;
using Helpers;

public class TestTracker : MonoBehaviour
{
    private static EyeMeasureDataWriter _eyeMeasureDataWriter;
    private static string _eyeMeasureDataFilename;
    
    /// <summary>
    /// Scene start: called once scene is loaded
    /// </summary>
    void Start()
    {
        // create the necessary stream writer instances for measure data & meta data
        _eyeMeasureDataFilename = DateTime.Now.ToString("yyyyMMdd_HHmm") + _suffixMeasureData + ".csv";
        _eyeMeasureDataWriter = new EyeMeasureDataWriter(_eyeMeasureDataFilename);

        SRanipal_Eye_v2.WrapperRegisterEyeDataCallback(Marshal.GetFunctionPointerForDelegate((SRanipal_Eye_v2.CallbackBasic)eyeCallback));
    }
    
    /// <summary>
    /// Cleanup data writer and SRanipal.
    /// </summary>
    void OnApplicationQuit()
    {
        _eyeMeasureDataWriter.Close();
        _eyeMetaDataWriter.Close();

        SRanipal_Eye_v2.WrapperUnRegisterEyeDataCallback(Marshal.GetFunctionPointerForDelegate((SRanipal_Eye_v2.CallbackBasic)eyeCallback));
    }

    /// <summary>
    /// Callback for SRanipal eye tracking data
    /// </summary>
    /// <param name="eyeData">The SRanipal eye tracking data</param>
    private static void eyeCallback(ref EyeData_v2 eyeData)
    {
        EyeParameter eyeParameter = new EyeParameter();
        SRanipal_Eye_API.GetEyeParameter(ref eyeParameter);

        // append the new data to the csv file
        _eyeMeasureDataWriter.AppendRow(DateTime.Now, TargetDot, TargetEye, eyeData, eyeParameter);
    }
}

 

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