Prediction Analysis of Optical Tracker Parameters using Machine Learning Approaches for efficient Head Tracking AMAN KATARIA1, SMARAJIT GHOSH1, VINOD KARAR2 1 Department of Electrical and Instrumentation Engineering, Thapar University, Patiala-147004, Punjab, India 2 Department of Optical Devices and Systems, CSIR-Central Scientific Instruments Organization, Chandigarh, India A head tracker is a crucial part of the head mounted display systems, data under different light intensity of the environment as it tracks the head of the pilot in the plane/cockpit simulator. The and distance between transmitter and receiver [4]. operational flaws of head trackers are also dependent on different According to the variations in environmental conditions, environmental conditions like different lighting conditions and stray appropriate number of trackers could be incorporated in a light interference. In this letter, an optical tracker has been employed to gather the 6-DoF data of head movements under different HMDs. Also in the aircraft simulator, it can help to choose environmental conditions. Also, the effect of different environmental the appropriate optical tracker according to the conditions and variation in distance between the receiver and optical environmental condition of simulator bed. transmitter on the 6-DoF data was analyzed. Machine learning has been used to great extent in Keywords: Machine Learning, Head Tracking, Random Forest, predicting mathematical and statistical optimization [5]. Optical Head Tracking, Aviation In the proposed work, four methods of machine learning applied to predict the 6-DoF data under different light Introduction: Head tracking has always been a intensities and the distance between transmitter significant part in designing of Head mounted display (infrared light source) and receiver (optical receiver). Six systems (HMDs). HMDs are considered as integral part DOF directions of head tracking are analyzed for different of fighter aircraft avionics. A head tracker is a crucial environmental conditions. For predicting the output, part of the HMDs, as it tracks the head of the pilot in the Random forest, Neural networks, Generalized linear plane/cockpit simulator to synchronize the view of outer model (GLM) and Support vector machine (SVM) are world with the view in the HMDs. There are various used. To determine the stableness and robustness of the types of head trackers which work with different best method of prediction, the K-fold cross validation is tracking techniques. Their operational flaws are also performed [6]. dependent on different environmental conditions which are different lighting conditions and stray light Remaining paper is structured with Section 1 interference. presenting the experimental setup, Section 2 represents Tracking can be positional or orientation in terms of the methodology used. Model evaluation is described in coordinates and when both are combined, the system is section 3. Results are discussed in section 4. Finally recognized as six degrees of freedom (6-DoF) system [1]. conclusion and future scope is presented in section 5 and Directions of head tracking in a 6 DOF system are X, Y, and section 6 respectively. Z known as positional coordinates and Roll, Yaw and Pitch known as orientation coordinates. TrackIRTM 5 Optical 1. Experimental Setup: For carrying out desired head tracker is used to track the six DOF directions of head experimentation conditions, the Cockpit Simulator is movement. TrackIRTM 5 optical tracker acts as a source to used. It comprised of pilot seat at designated distance generate the Infrared (IR) light. The incoming IR light is from the transmitter. The aircraft canopy covered the reflected back by the three retro-reflective markers, which head up display along with the optical transmitter. The are assembled in the TrackClip which is placed on the receiver (infrared retro-reflector) was mounted on the helmet/head of the pilot. The reflected IR light is detected user cap. The diffused light source controlled the by the infrared camera present in TrackIRTM 5, which then ambient light variations, while the pilot movement tracks the positional and orientation coordinates of the simulated the distances between the transmitter and head of the pilot. the receiver. TrackIR 5™ is used to track the head Experiments were conducted under different light movements in Display Simulator. The light intensity intensities (LI) and different distance range values was measured through Lux Meter (Model TES 1332 between transmitter and receiver (tracker) on which the Digital Lux Meter). performance of an optical tracker strongly depends. Generally, the expected performance of an optical tracker diverges largely if the stray light interference is more. Each optical tracker has limited work capacity under some particular LI [2]. In the experiment, the 6-DoF data is predicted through different machine learning methods under different light intensity and distance variation between sensor and transmitter to virtually judge the performance of an optical tracker [3]. A desirable predictive method is required which can predict the 6-DoF a) Display Simulator Fig.4. Experiment conducted under 111 lux light intensity with different distances 25cm, 50cm, 75cm and 100cm marked as 1, 2, 3 and 4 respectively. ™ Fig.1. Display Simulator with optical tracker TrackIR 5 (Shown in red circle) at CSIR- CSIO Fig.2. Experiment conducted under 3 lux light intensity Fig.5. Experiment conducted under 165 lux light intensity with different distances 25cm, 50cm, 75cm and 100cm with different distances 25cm, 50cm, 75cm and 100cm marked as 1, 2, 3 and 4 respectively. marked as 1, 2, 3 and 4 respectively. Fig.3. Experiment conducted under 75 lux light intensity with different distances 25cm, 50cm, 75cm and 100cm marked as 1, 2, 3 and 4 respectively Fig.6 Lux meter readings under different light intensity. 2. Methodology Used is measured in Lux (lx). The experiments are conducted for light intensity varying form 4 lux to 166 lux. In the 2.1 Description of Data Set and its Features experimentation, the distance between the pilot’s head (transmitter is located on cap worn on head) and the Data set have been modeled after performing receiver are kept in four distances: 25cm, 50cm, 75cm and experiments under different conditions viz. variation in 100cm. light intensity and variation in distances between the transmitter and the receiver. Description regarding 2.3 Feature Description movements of head in optical head tracking used in the experiment has been described in Table I. Values of light Six physical DOF directions are extensively used in the intensity, distances between transmitter and receiver experimentation and subsequent analysis. The X and sample values of 6-DOF head tracking coordinates coordinate in this case is the translation of the body along are provided in Table- II. X-axis also known as forward and backward translation. Forward translation leads to positive value and backward Table- I: Description of the movements of head recorded by translation leads to negative values. The Y coordinate is an Optical Tracker the translation of the body along Y-axis also known as left DoF Information and right translation. Right translation leads to positive X Forward and backward translational value and left translation leads to negative values. Z coordinate of the pilot’s head coordinate is the coordinate of translation of the body along Y Left and right translational coordinate of the Z-axis also known as up and down translation. Up pilot’s head translation leads to positive value and down translation Z Up and Down translational coordinate of the leads to negative value. The rotational coordinates are pilot’s head Yaw, Pitch and Roll. Yaw is the rotation along Z-axis and Yaw Rotational coordinate of the pilot’s head is measured in degrees. Roll is the rotation along X-axis along Z-axis and is measured in degrees and Pitch is the rotation along Pitch Rotational coordinate of the pilot’s head Y-axis and is measured in degrees. The rotational matrixes along Y-axis of the rotational coordinates are given below: Roll Rotational coordinate of the pilot’s head along X-axis Light Distanc Yaw Pitch Roll X Y Z intensity e (in (in lux) cm) 3 25 -18.2 3.8 -17.8 -4.5 4.1 13.47 3 50 -20.5 -1.7 -7.8 0.2 0.7 -10.3 3 75 -23.5 -12.78 -2.67 -13.6 -0.2 3.97 3 100 5.1 -14.44 -2.9 6 0.7 -5.13 75 25 -54.3 1.1 -0.6 -2.8 0.51 6.05 75 50 -49 -1.4 -1.8 -1.2 1.4 2.95 75 75 -8.8 2 -4.5 -1.9 1.3 -0.16 Fig.7 Prototype view of Optical Head tracker [7] 75 100 -11.6 1 -3.8 0.3 -1.9 -12.36 111 25 -13.1 -2.8 0.1 -7.6 3.2 5.66 111 50 -7.4 -3 0 -6.2 3.3 5.38 111 75 -2 -2.8 -0.4 -1.1 3 6.46 111 25 -16 -2.8 -0.4 2 2.9 -2.15 165 50 9.3 -6.6 2.4 0.6 2.5 -9.43 165 25 9.7 -6.1 2 1 2 -11.21 165 75 9.43 -6.67 2.4 0.6 2.5 -9.43 165 100 -10.22 -7.99 -1.8 5 2 -7.76 Table 2. Sample set of Data 2.2 Quantitative Assessment Experiments conducted with light intensity and distance variation between the transmitter and the receiver helps in predication of the desirable conditions in which optical tracker give satisfactory output. Light intensity is measured as the rate at which energy of light is delivered Fig.8 Methodology used per unit surface per unit time per unit area. Light intensity 2.4 Approach candidate pool.