Infrared Tracking System Research Articles

An Experimental Approach for the Quantitative Assessment of Downstream Swimming Fish Behavior

ABSTRACTBehavior of fish influences the mortality risk during turbine and pump passages. Knowledge about species‐specific behavior and its triggers is necessary for improving numerical models and the development of autonomous sensor probes to estimate fish mortality in turbines and pumps. A primary objective of the RETERO project is the study of fish behavior in hydraulic conditions similar to turbine and pump intakes in controlled conditions. For this purpose, an experimental conduit was constructed at the Hubert‐Engels Laboratory of the TUD Dresden University of Technology (Germany) equipped with a 3D camera infrared tracking system. The conduit was designed to model hydraulic conditions typical for turbine and pump intakes. In the experimental setup, the effects of flow velocities exceeding the maximum swim speed of fish, as well as spatial velocity gradients and illumination conditions on the fish behavior are studied. The data from brown trout (Salmo trutta) allow for an analysis of how these fish react to flow accelerations and velocities surpassing their sprint speed, using quantitative metrics for movement and activity. An initial evaluation of these experiments highlights the potential of this approach for further research.

Finding a Husband: Using Explainable AI to Define Male Mosquito Flight Differences.

Mosquito-borne diseases account for around one million deaths annually. There is a constant need for novel intervention mechanisms to mitigate transmission, especially as current insecticidal methods become less effective with the rise of insecticide resistance among mosquito populations. Previously, we used a near infra-red tracking system to describe the behaviour of mosquitoes at a human-occupied bed net, work that eventually led to an entirely novel bed net design. Advancing that approach, here we report on the use of trajectory analysis of a mosquito flight, using machine learning methods. This largely unexplored application has significant potential for providing useful insights into the behaviour of mosquitoes and other insects. In this work, a novel methodology applies anomaly detection to distinguish male mosquito tracks from females and couples. The proposed pipeline uses new feature engineering techniques and splits each track into segments such that detailed flight behaviour differences influence the classifier rather than the experimental constraints such as the field of view of the tracking system. Each segment is individually classified and the outcomes are combined to classify whole tracks. By interpreting the model using SHAP values, the features of flight that contribute to the differences between sexes are found and are explained by expert opinion. This methodology was tested using 3D tracks generated from mosquito mating swarms in the field and obtained a balanced accuracy of 64.5% and an ROC AUC score of 68.4%. Such a system can be used in a wide variety of trajectory domains to detect and analyse the behaviours of different classes, e.g., sex, strain, and species. The results of this study can support genetic mosquito control interventions for which mating represents a key event for their success.

Research on monostation passive location technology based on infrared tracking system

The ability to track and locate aerial targets is of great significance to target monitoring and recognition, as well as other applications. The traditional infrared tracking system needs the assistance of active ranging methods, such as laser and radar, or binocular vision and multistation detection methods for positioning. Based on high-resolution infrared tracking systems, which measure the target temperature and angle, and the law that target temperature changes with height, a monostation passive target location method based on infrared quantitative detection is proposed. The theoretical model of target location, which comprehensively considers the factors of temperature retrieval, aerodynamic heating, and atmosphere, is established. The location experiment is conducted with the developed high-resolution infrared tracking system. Compared with the automatic dependent surveillance-broadcast data of the actual target, the relative error of the ranging is <5 % . The error sources of this method are simulated and analyzed, and the simulation of the location distance and the error analysis of the long-distance target are conducted. Results show that the proposed method effectively locates the target. The method improves the monostation location ability of the infrared system and has a certain application value.

DESIGN AND IMPLEMENTATION OF ANTI-TANK GUIDED-MISSILE (ATGM) CONTROL SYSTEM USING SEMI-AUTOMATIC COMMAND LINE OF SIGHT (SACLOS) METHOD BASED ON DIGITAL IMAGE PROCESSING

&lt;div&gt;&lt;p class="Els-history-head"&gt;The Anti-Tank Guided-Missile (ATGM) system has a very important role in the modern battlefield. This system proved its effectiveness in many modern conflicts such as the Syrian Civil War and Nagorno-Karabakh War. The ATGM system has a very simple electronic and mechanism but it has a very high level of accuracy and precision. One of the control methods used in ATGM is SACLOS method. This method tracks missile position by detecting an infrared lamp that is placed on the missile tail. The tracking system sends control signals to the missile as a result of the correction of the missile position when flying. The infrared tracking system in this research was made using a modified OV5647 camera with the addition of a 940 nm narrow bandpass filter. There are 3 cameras with 1x, 8x, and 16x magnifications which are accessed using 3 Raspberry Pi boards. X and y coordinate data of the infrared lamp is sent to the airframe using wireless telemetry. Atmega328 microcontroller process x and y coordinate data into input proportional control. The result of this research is the prototype of an anti-tank missile control system with an infrared tracking instrument capable track a series of 88 infrared LEDs as far as 997.16 meters with a tracking speed of 90.11 FPS. The threshold parameters of image processing using luminance of YUV color space has a range of 240-255. The control parameter Kp=7 is used in wind tunnel testing with airspeed 20 m/s capable of directing airframe motion to the telescope's crosshairs.&lt;/p&gt;&lt;/div&gt;

Infrared Dim and Small Target Detection Based on Greedy Bilateral Factorization in Image Sequences

Fast and stable detection of dim and small infrared (IR) targets in complex backgrounds has important practical significance for IR search and tracking system. The existing small IR target detection methods usually fail or cause a high probability of false alarm in the highly heterogeneous and complex backgrounds. Continuous motion of a target relative to the background is important information regarding detection. In this article, a low-rank and sparse decomposition method based on greedy bilateral factorization is proposed for IR dim and small target detection. First, by analyzing the complex structure information of IR image sequences, the target is regarded as an independent sparse motion structure and an efficient optimization algorithm is designed. Second, the greedy bilateral factorization strategy is adopted to approximate the low-rank part of the algorithm, which significantly accelerates the efficiency of the algorithm. Extensive experiments demonstrate that the proposed method has better detection performance than the existing methods. The proposed method can still detect targets quickly and stably especially in complex scenes with weak signal-to-noise ratio.

Design of Navigation System for Liver Surgery Guided by Augmented Reality

The traditional surgical navigation system combining preoperative CT and intraoperative ultrasound is widely used in open hepatectomy, but the problem of this system is that there are some errors in terms of the precision of the time and the space during the surgery. In order to solve the above problems, this paper introduces augmented reality technology into the surgical navigation system. In order to accurately describe the biomechanical characteristics of the liver and let the navigation system perform more accurately, this paper uses Tetgen to perform tetrahedral partition on the triangle mesh data obtained after the three-dimensional CT was reconstructed, and then the surface mesh data and the internal tetrahedral data were obtained and they were used to describe a whole liver model. The surface triangle mesh data is used to render graphics and describe the surface topology change, and the internal tetrahedral data combined with mass-spring theory is used to simulate deformation. Subsequently, the ex vivo pig liver was used to experimentally verify the accuracy of gravity deformation of the liver model, and the results show that the error was mainly distributed between −2mm and −2.5mm. At the same time, this paper uses the NDI Polaris infrared tracking system to carry out precision experiments on the augmented reality module, and the measured error is 1.55± 0.29mm. Finally, various modules of the system are integrated to finish the experiment in which the ring-shaped lesions are cut from the ex vivo pig liver with the aid of augmented reality. The experimental error is 0± 1.26mm, and with the assistance of the general purpose graphics processing unit (GPGPU), the refresh rate is above 200FPS. The results prove that the liver surgery navigation system proposed in this paper is excellent in terms of real-time performance and accuracy, which can help doctors accurately locate the tumor during surgery and perform ideal resection.

An Autonomous Docking Mechanism for Vertical Lift Unmanned Aircraft

Abstract Unmanned aerial vehicles are increasingly being tasked to connect to payload objects or docking stations for the purposes of package transport or recharging. However, autonomous docking creates challenges in that the air vehicle must precisely position itself with respect to the dock, oftentimes in the presence of uncertain winds and measurement errors. This paper describes an autonomous docking mechanism comprising a static ring and actuated legs, coupled with an infrared tracking device for closed-loop docking maneuvers. The dock’s unique mechanical design enables precise passive positioning such that the air vehicle slides into a precise location and orientation in the dock from a wide range of entry conditions. This leads to successful docking in the presence of winds and sensor measurement errors. A closed-loop infrared tracking system is also described in which the vehicle tracks an infrared beacon located on the dock during the descent to landing. A detailed analysis is presented describing the interaction dynamics between the aircraft and the dock, and system parameters are optimized through the use of trade studies and Monte Carlo analysis with a three degree-of-freedom simulation model. Experimental results are presented demonstrating successful docking maneuvers of an autonomous air vehicle in both indoor and outdoor environments. These repeatable docking experiments verify the robustness and practical utility of the dock design for a variety of emerging applications.

Three-dimensional location of target fish by monocular infrared imaging sensor based on a L–z correlation model

Monitoring of fish behavior has drawn extensive attention in pharmacological research, water environmental assessment, bio-inspired robot design and aquaculture. Given that an infrared sensor is low cost, no illumination limitation and electromagnetic interference, interest in its use in behavior monitoring has grown considerably, especially in 3D trajectory monitoring to quantify fish behavior on the basis of near infrared absorption of water. However, precise position of vertical dimension (z) remains a challenge, which greatly impacts on infrared tracking system accuracy. Hence, an intensity (L) and coordinate (z) correlation model was proposed to overcome the limitation. In the modelling process, two cameras (top view and side view) were employed synchronously to identify the 3D coordinate of each fish (x-y and z, respectively), and the major challenges were the distortion caused by the perspective effect and the refraction at water boundaries. Therefore, a coordinate correction formulation was designed firstly for the calibration. Then the L–z correlation model was established based on Lambert's absorption law and statistical data analysis, and the model was estimated through monitoring 3D trajectories of four fishes during the day and night. Finally, variations of individuals and limits of the depth detection of the model were discussed. Compared with previous studies, the favorable prediction performance of the model is achieved for 3D trajectory monitoring, which could provide some inspirations for fish behavior monitoring, especially for nocturnal behavior study.

Feasibility of infrared tracking of beating heart motion for robotic assisted beating heart surgery.

Accurate tracking of the heart surface motion is a major requirement for robot assisted beating heart surgery. The feasibility of a stereo infrared tracking system for measuring the free beating heart motion was investigated by experiments on a heart motion simulator, as well as model surgery on a dog. Simulator experiments revealed a high tracking accuracy (81 μm root mean square error) when the capturing times were synchronized and the tracker pointed at the target from a 100 cm distance. The animal experiment revealed the applicability of the infrared tracker with passive markers in practical heart surgery conditions. With the current technology, infrared tracking with passive markers might be the optimal solution for accurate, fast, and reliable tracking of heart motion during robot assisted beating heart surgery.

Robust Real-Time Needle Tracking in 2-D Ultrasound Images Using Statistical Filtering

Percutaneous image-guided tumor ablation is a minimally invasive surgical procedure for the treatment of malignant tumors using a needle-shaped ablation probe. Automating the insertion of a needle by using a robot could increase the accuracy and decrease the execution time of the procedure. Extracting the needle tip position from the ultrasound (US) images is of paramount importance for verifying that the needle is not approaching any forbidden regions (e.g., major vessels and ribs), and could also be used as a direct feedback signal to the robot inserting the needle. A method for estimating the needle tip has previously been developed combining a modified Hough transform, image filters, and machine learning. This paper improves that method by introducing a dynamic selection of the region of interest in the US images and filtering the tracking results using either a Kalman filter or a particle filter. Experiments where a biopsy needle has been inserted into a phantom by a robot have been conducted, guided by an infrared tracking system. The proposed method has been accurately evaluated by comparing its estimations with the needle tip’s positions manually detected by a physician in the US images. The results show a significant improvement in precision and more than 85% reduction of 95th percentile of the error compared with the previous automatic approaches. The method runs in real time with a frame rate of 35.4 frames/s. The increased robustness and accuracy can make our algorithm usable in autonomous surgical systems for needle insertion.

Intra-fraction respiratory motion and baseline drift during breast Helical Tomotherapy

Background and purposeTo investigate the intra-fraction breast motion during long-lasting treatments of breast cancer with Helical Tomotherapy by means of an optical tracking system. Materials and methodsA set of seven radio-transparent passive markers was placed on the thoraco-abdominal surface of twenty breast cancer patients and tracked by an infrared tracking system. A continuous non-invasive monitoring of intra-fraction motion from patient setup verification and correction to the end of radiation delivery was thus obtained. The measured displacements were analysed in terms of cyclic respiratory motion and slow baseline drift. ResultsThe average monitoring time per patient was 15.57min. The breathing amplitude of the chest was less than 2mm, on average, along all anatomical directions. The baseline drift of the body led to more significant setup uncertainties than the respiratory motion. The main intra-fraction baseline drifts were in posterior and inferior directions and occurred within the first eight minutes of monitoring. Considering the intra-fraction motion only, the resultant clinical-to-planning target volume safety margins are highly patient-specific and largely anisotropic. ConclusionThe non-respiratory motion occurring during prolonged treatments induces notable uncertainties. Non-invasive continuous monitoring of patient setup variations including baseline drifts is recommended in order to minimize dosimetric deviations, which might jeopardize the therapeutic ratio between target coverage and the sparing of organs at risk.

Sci‐Fri PM: Radiation Therapy, Planning, Imaging, and Special Techniques ‐ 09: Impact of the distance of reflective markers from linac isocenter on the positional accuracy of an infrared tracking system

Purpose:The HexaPOD™ six degree of freedom couchtop is equipped with an optical tracking system, consisting of a stereoscopic camera and a reference frame (RF) carrying infrared reflective markers. The manufacturer recommends placing the RF within 50 cm from linac isocenter (ISO), which is a serious limitation since the RF does not fit around the shoulders of most brain patients. This study quantifies the impact of extended RF distances from ISO on positional accuracy.Methods:An in‐house tool with an estimated resolution of 0.3 mm and 0.1° was used. It is a large cube and a mathematical model of HexaPOD motion to determine the intersection of room lasers with the ruled cube edges. Combinations of translations (±1 and ±3 cm) and rotations (±2.5°) were executed on two HexaPOD couchtops for multiple RF distances from ISO (35 to 77 cm). For each combination, ten laser readings were fed into a least squares algorithm to determine the executed translations and rotations while minimizing operator reading errors.Results:The usable tracking volume is up to an RF distance of 82 cm from ISO. Positional accuracy of the HexaPOD/iGuide system is 0.6 mm and 0.1° (95% confidence). Positional accuracy variations versus RF distance from ISO are statistically insignificant (p = 0.05). Our results generally confirm recent internal estimates by the manufacturer (for future release).Conclusions:RF distances up to 77 cm from ISO are clinically acceptable, provided performing a patient safety study with a verification scan.

TH-AB-202-11: Spatial and Rotational Quality Assurance of 6DOF Patient Tracking Systems

Purpose: External tracking systems used for patient positioning and motion monitoring during radiotherapy are now capable of detecting both translations and rotations (6DOF). In this work, we develop a novel technique to evaluate the 6DOF performance of external motion tracking systems. We apply this methodology to an infrared (IR) marker tracking system and two 3D optical surface mapping systems in a common tumor 6DOF workspace. Methods: An in-house designed and built 6DOF parallel kinematics robotic motion phantom was used to follow input trajectories with sub-millimeter and sub-degree accuracy. The 6DOF positions of the robotic system were then tracked and recorded independently by three optical camera systems. A calibration methodology which associates the motion phantom and camera coordinate frames was first employed, followed by a comprehensive 6DOF trajectory evaluation, which spanned a full range of positions and orientations in a 20×20×16 mm and 5×5×5 degree workspace. The intended input motions were compared to the calibrated 6DOF measured points. Results: The technique found the accuracy of the IR marker tracking system to have maximal root mean square error (RMSE) values of 0.25 mm translationally and 0.09 degrees rotationally, in any one axis, comparing intended 6DOF positions to positions measured by the IR camera. The 6DOF RSME discrepancy for the first 3D optical surface tracking unit yielded maximal values of 0.60 mm and 0.11 degrees over the same 6DOF volume. An earlier generation 3D optical surface tracker was observed to have worse tracking capabilities than both the IR camera unit and the newer 3D surface tracking system with maximal RMSE of 0.74 mm and 0.28 degrees within the same 6DOF evaluation space. Conclusion: The proposed technique was effective at evaluating the performance of 6DOF patient tracking systems. All systems examined exhibited tracking capabilities at the sub-millimeter and sub-degree level within a 6DOF workspace.

Improved setup and positioning accuracy using a three-point customized cushion/mask/bite-block immobilization system for stereotactic reirradiation of head and neck cancer.

The purpose of this study was to investigate the setup and positioning uncertainty of a custom cushion/mask/bite‐block (CMB) immobilization system and determine PTV margin for image‐guided head and neck stereotactic ablative radiotherapy (HN‐SABR). We analyzed 105 treatment sessions among 21 patients treated with HN‐SABR for recurrent head and neck cancers using a custom CMB immobilization system. Initial patient setup was performed using the ExacTrac infrared (IR) tracking system and initial setup errors were based on comparison of ExacTrac IR tracking system to corrected online ExacTrac X‐rays images registered to treatment plans. Residual setup errors were determined using repeat verification X‐ray. The online ExacTrac corrections were compared to cone‐beam CT (CBCT) before treatment to assess agreement. Intrafractional positioning errors were determined using prebeam X‐rays. The systematic and random errors were analyzed. The initial translational setup errors were −0.8±1.3 mm, −0.8±1.6 mm, and 0.3±1.9 mm in AP, CC, and LR directions, respectively, with a three‐dimensional (3D) vector of 2.7±1.4 mm. The initial rotational errors were up to 2.4° if 6D couch is not available. CBCT agreed with ExacTrac X‐ray images to within 2 mm and 2.5°. The intrafractional uncertainties were 0.1±0.6 mm, 0.1±0.6 mm, and 0.2±0.5 mm in AP, CC, and LR directions, respectively, and 0.0∘±0.5°, 0.0∘±0.6°, and −0.1∘±0.4∘ in yaw, roll, and pitch direction, respectively. The translational vector was 0.9±0.6 mm. The calculated PTV margins mPTV(90,95) were within 1.6 mm when using image guidance for online setup correction. The use of image guidance for online setup correction, in combination with our customized CMB device, highly restricted target motion during treatments and provided robust immobilization to ensure minimum dose of 95% to target volume with 2.0 mm PTV margin for HN‐SABR.PACS number(s): 87.55.ne

Feasibility Study of Real Time Ultrasound Intrafractional Monitoring in Liver Stereotactic Body Radiation Therapy Underactive Breathing Control

Stereotactic body radiation therapy (SBRT) allows delivery of high doses to liver tumor with steep dose gradients to surrounding normal tissue and thus limits risk of liver toxicity. Intra-fraction target motion remains one of the major sources of uncertainty in liver SBRT. It blurs the planned dose distribution and thus undermines the purpose of SBRT. Ultrasound is a cost effective and non-ionizing approach for motion monitoring. In this study, we investigated the feasibility of an existing ultrasound prostate monitoring system for liver SBRT under active breathing control (ABC) and its monitoring accuracy in simulated phantom experiment. An abdominal ultrasound phantom with six tumors inside the liver was used. The phantom was secured on a programmable respiratory motion platform. A 4D probe was modified for transabdominal imaging with flexible infrared tracking angle. A medical grade arm and bridge secure system (ABS) was developed to hold ultrasound probe. The motion platform was programmed to perform repeated mechanical movement to simulate ABC patient motion. Platform was programmed to move in superior-inferior direction, which is the major tumor motion direction observed in our patients. The movement step was set to be 0 mm with 20 seconds followed by 10 mm in inferior direction with 20 seconds in one cycle to simulate the expiration and inspiration breath hold phases of the ABC. In total of 10 cycles of movement were repeated and the expiration ultrasound was taken as the reference image. 4D ultrasound images were then acquired continuously for monitoring. For the 10 cycles of movements of 10 mm in inferior direction, the average real-time movement distance reported by 4D motion monitoring system was 9.92±0.13 mm and with maximum deviation less than 0.3 mm compared with programmed step. No probe fixation alert was detected during the whole experiment by the infrared tracking system. Our 4D motion monitoring system was able to accurately recover the liver tumor motion in our phantom study. Our ABS system is able to hold the probe steady during the whole motion simulation. This suggests with modification, current 4D prostate ultrasound system can be applied to real-time intra-fractional motion monitoring in liver SBRT with ABC.

Accuracy of a hexapod parallel robot kinematics based external fixator.

Different hexapod-based external fixators are increasingly used to treat bone deformities and fractures. Accuracy has not been measured sufficiently for all models. An infrared tracking system was applied to measure positioning maneuvers with a motorized Precision Hexapod® fixator, detecting three-dimensional positions of reflective balls mounted in an L-arrangement on the fixator, simulating bone directions. By omitting one dimension of the coordinates, projections were simulated as if measured on standard radiographs. Accuracy was calculated as the absolute difference between targeted and measured positioning values. In 149 positioning maneuvers, the median values for positioning accuracy of translations and rotations (torsions/angulations) were below 0.3 mm and 0.2° with quartiles ranging from -0.5 mm to 0.5 mm and -1.0° to 0.9°, respectively. The experimental setup was found to be precise and reliable. It can be applied to compare different hexapod-based fixators. Accuracy of the investigated hexapod system was high.

Calcium phosphate particulates increase friction in the rat knee joint

Basic calcium phosphate (BCP) particulates are commonly found in cartilage and synovial fluid of osteoarthritis (OA) joints with the amount of BCP correlating with knee OA severity. How cartilage mineralization affects joint degeneration has yet to be determined. The objective of this study was to determine whether BCP in the synovial fluid affects the rat knee joint coefficient of friction (COF). The COFs of knees from both hind limbs of four mature male rats were measured post mortem using a pendulum apparatus with an infrared tracking system. The three conditions evaluated were (1) the naïve state, (2) after the injection of 100 μL of phosphate buffered saline (PBS) (sham) and (3) after the injection of 100 μL of a 1 mg/mL BCP suspension. The decrease in the pendulum amplitude (decay) was fit using two friction models: (1) a one parameter Stanton linear decay model and (2) a two parameters combination Stanton linear decay and viscous damping exponential decay model. The COF increased 17.6% after injection of BCP compared to the naïve (P = 0.0012) and 16.0% compared to the saline injected (P = 0.0018) joints as derived from the one parameter model. The COF did not differ between naïve and saline injected joints. Results from the two parameters model showed a similar increase in COF after injection of BCP while the viscous damping was not significantly different between conditions. The increased joint friction with BCP particulates suggests BCPs may play a role in articular surface degradation and OA development.

Aerial-target detection using the recursive temporal profile and spatiotemporal gradient pattern in infrared image sequences

A new spatiotemporal target detection method that utilizes the recursive temporal profile (RTP) and the spatiotemporal gradient pattern (STGP) is proposed for infrared (IR) image sequence. In the IR search and tracking system, long-distance aerial targets compared with short-distance aerial targets appear to be composed of several pixels with no special shapes and their movements are slow. Considering the characteristics of aerial targets, an algorithm based on the STGP and fuzzy-set theory is proposed to detect long-distance aerial targets while the recursive temporal profile algorithm based on the temporal profile and mean estimation is proposed to detect short-distance aerial targets. In addition, the RTP and the STGP are combined to detect the aerial targets that exist at diverse distances in the IR image sequence. The performance of the proposed method is examined by using the receiver operating characteristic curve. The experiment results show that the proposed method performs better than the existing methods in terms of target detection and clutter removal.

Kinetics of the cervical spine in pediatric and adult volunteers during low speed frontal impacts

Previous research has quantified differences in head and spinal kinematics between children and adults restrained in an automotive-like configuration subjected to low speed dynamic loading. The forces and moments that the cervical spine imposes on the head contribute directly to these age-based kinematic variations. To provide further explanation of the kinematic results, this study compared the upper neck kinetics – including the relative contribution of shear and tension as well as flexion moment – between children (n=20, 6–14yr) and adults (n=10, 18–30yr) during low-speed (<4g, 2.5m/s) frontal sled tests. The subjects were restrained by a lap and shoulder belt and photo-reflective targets were attached to skeletal landmarks on the head, spine, shoulders, sternum, and legs. A 3D infrared tracking system quantified the position of the targets. Shear force (Fx), axial force (Fz), bending moment (My), and head angular acceleration (θ̈head) were computed using inverse dynamics. The method was validated against ATD measured loads. Peak Fz and θ̈head significantly decreased with increasing age while My significantly increased with increasing age. Fx significantly increased with age when age was considered as a univariate variable; however when variations in head-to-neck girth ratio and change in velocity were accounted for, this difference as a function of age was not significant. These results provide insight into the relationship between age-based differences in head kinematics and the kinetics of the cervical spine. Such information is valuable for pediatric cervical spine models and when scaling adult-based upper cervical spine tolerance and injury metrics to children.

Accurate Infrared Tracking System for Immersive Virtual Environments

In large-scale immersive virtual reality (VR) environments, such as a CAVE, one of the most common problems is tracking the position of the user’s head while he or she is immersed in this environment to reflect perspective changes in the synthetic stereoscopic images. In this paper, the authors describe the theoretical foundations and engineering approach adopted in the development of an infrared-optical tracking system designed for large scale immersive Virtual Environments (VE) or Augmented Reality (AR) settings. The system is capable of tracking independent retro-reflective markers arranged in a 3D structure in real time, recovering all possible 6DOF. These artefacts can be adjusted to the user’s stereo glasses to track his or her head while immersed or used as a 3D input device for rich human-computer interaction (HCI). The hardware configuration consists of 4 shutter-synchronized cameras attached with band-pass infrared filters and illuminated by infrared array-emitters. Pilot lab results have shown a latency of 40 ms when simultaneously tracking the pose of two artefacts with 4 infrared markers, achieving a frame-rate of 24.80 fps and showing a mean accuracy of 0.93mm/0.51º and a mean precision of 0.19mm/0.04º, respectively, in overall translation/rotation, fulfilling the requirements initially defined.