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An Inertial and Optical Sensor Fusion Approach for Six Degree-of-Freedom Pose Estimation.

He C, Kazanzides P, Sen HT, Kim S, Liu Y - Sensors (Basel) (2015)

Bottom Line: In contrast, inertial sensing does not require line-of-sight but is subject to drift, which may cause large cumulative errors, especially during the measurement of position.When all the markers are occluded, the position tracking relies on the inertial sensors that are bias-corrected by the optical tracking system.Experiments are performed with an augmented reality head-mounted display (ARHMD) that integrates an optical tracking system (OTS) and inertial measurement unit (IMU).

View Article: PubMed Central - PubMed

Affiliation: Beijing Engineering Research Center of Mixed Reality and Advanced Display, School of Optoelectronics, Beijing Institute of Technology, Beijing 100081, China. wosipo007@163.com.

ABSTRACT
Optical tracking provides relatively high accuracy over a large workspace but requires line-of-sight between the camera and the markers, which may be difficult to maintain in actual applications. In contrast, inertial sensing does not require line-of-sight but is subject to drift, which may cause large cumulative errors, especially during the measurement of position. To handle cases where some or all of the markers are occluded, this paper proposes an inertial and optical sensor fusion approach in which the bias of the inertial sensors is estimated when the optical tracker provides full six degree-of-freedom (6-DOF) pose information. As long as the position of at least one marker can be tracked by the optical system, the 3-DOF position can be combined with the orientation estimated from the inertial measurements to recover the full 6-DOF pose information. When all the markers are occluded, the position tracking relies on the inertial sensors that are bias-corrected by the optical tracking system. Experiments are performed with an augmented reality head-mounted display (ARHMD) that integrates an optical tracking system (OTS) and inertial measurement unit (IMU). Experimental results show that under partial occlusion conditions, the root mean square errors (RMSE) of orientation and position are 0.04° and 0.134 mm, and under total occlusion conditions for 1 s, the orientation and position RMSE are 0.022° and 0.22 mm, respectively. Thus, the proposed sensor fusion approach can provide reliable 6-DOF pose under long-term partial occlusion and short-term total occlusion conditions.

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Related in: MedlinePlus

Workflow of the hybrid tracking system.
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sensors-15-16448-f003: Workflow of the hybrid tracking system.

Mentions: In order to combine the outputs from OTS and IMU, the two tracking units are registered with a calibration procedure [23] through which the transformation matrix between the two units is achieved. The reference frame consists of three markers attached to a plastic board and is assumed to remain stationary during the procedure (more precisely, all other measurements are made relative to this frame so, without loss of generality, it can be assumed to be stationary). The test setup also includes a surgical instrument that contains three tracked marker points, though in a smaller physical arrangement. The workflow of the hybrid tracking system is shown in Figure 3, which finally outputs the 6-DOF pose including 3-DOF orientation and 3-DOF position. The execution time of the sensor fusion approach is approximately 0.5 ms. Note that our HMD setup combines the IMU with the OTS, but the proposed method would also apply to setups where the IMU is attached to the marker frame(s). The disadvantage of the latter one is the increased complexity of the frame (i.e., IMU electronics that require a power source and wired or wireless communication), but the advantage is that the proposed sensor fusion method can be used for multiple frames.


An Inertial and Optical Sensor Fusion Approach for Six Degree-of-Freedom Pose Estimation.

He C, Kazanzides P, Sen HT, Kim S, Liu Y - Sensors (Basel) (2015)

Workflow of the hybrid tracking system.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4541887&req=5

sensors-15-16448-f003: Workflow of the hybrid tracking system.
Mentions: In order to combine the outputs from OTS and IMU, the two tracking units are registered with a calibration procedure [23] through which the transformation matrix between the two units is achieved. The reference frame consists of three markers attached to a plastic board and is assumed to remain stationary during the procedure (more precisely, all other measurements are made relative to this frame so, without loss of generality, it can be assumed to be stationary). The test setup also includes a surgical instrument that contains three tracked marker points, though in a smaller physical arrangement. The workflow of the hybrid tracking system is shown in Figure 3, which finally outputs the 6-DOF pose including 3-DOF orientation and 3-DOF position. The execution time of the sensor fusion approach is approximately 0.5 ms. Note that our HMD setup combines the IMU with the OTS, but the proposed method would also apply to setups where the IMU is attached to the marker frame(s). The disadvantage of the latter one is the increased complexity of the frame (i.e., IMU electronics that require a power source and wired or wireless communication), but the advantage is that the proposed sensor fusion method can be used for multiple frames.

Bottom Line: In contrast, inertial sensing does not require line-of-sight but is subject to drift, which may cause large cumulative errors, especially during the measurement of position.When all the markers are occluded, the position tracking relies on the inertial sensors that are bias-corrected by the optical tracking system.Experiments are performed with an augmented reality head-mounted display (ARHMD) that integrates an optical tracking system (OTS) and inertial measurement unit (IMU).

View Article: PubMed Central - PubMed

Affiliation: Beijing Engineering Research Center of Mixed Reality and Advanced Display, School of Optoelectronics, Beijing Institute of Technology, Beijing 100081, China. wosipo007@163.com.

ABSTRACT
Optical tracking provides relatively high accuracy over a large workspace but requires line-of-sight between the camera and the markers, which may be difficult to maintain in actual applications. In contrast, inertial sensing does not require line-of-sight but is subject to drift, which may cause large cumulative errors, especially during the measurement of position. To handle cases where some or all of the markers are occluded, this paper proposes an inertial and optical sensor fusion approach in which the bias of the inertial sensors is estimated when the optical tracker provides full six degree-of-freedom (6-DOF) pose information. As long as the position of at least one marker can be tracked by the optical system, the 3-DOF position can be combined with the orientation estimated from the inertial measurements to recover the full 6-DOF pose information. When all the markers are occluded, the position tracking relies on the inertial sensors that are bias-corrected by the optical tracking system. Experiments are performed with an augmented reality head-mounted display (ARHMD) that integrates an optical tracking system (OTS) and inertial measurement unit (IMU). Experimental results show that under partial occlusion conditions, the root mean square errors (RMSE) of orientation and position are 0.04° and 0.134 mm, and under total occlusion conditions for 1 s, the orientation and position RMSE are 0.022° and 0.22 mm, respectively. Thus, the proposed sensor fusion approach can provide reliable 6-DOF pose under long-term partial occlusion and short-term total occlusion conditions.

Show MeSH
Related in: MedlinePlus