EXPERIMENTAL MOTION ANALYSIS VIA A STEREO-PHOTOGRAPHY TECHNIQUE: APPLICATION TO THE HUMAN JAW AND MECHANICAL LINKAGES.
Arthur G. ErdmanRichard ForstromFrank D. DormanFred AhlgrenRobert BeerRobert J. IsaacsonM. T. Speidel
2
Citation
0
Reference
12
Related Paper
Keywords:
Motion analysis
Cite
Position (finance)
Cite
Citations (0)
An eight-camera Optitrack motion capture system was evaluated by performing static, linear dynamic, and angular dynamic calibrations using marker distances associated with upper and lower extremity gait and wheelchair models. Data were analyzed to determine accuracy and resolution within a defined capture volume using a standard Cartesian reference system. Static accuracy ranged from 99.31 to 99.90%. Static resolution ranged from 0.04 ± 0.15 to 0.63 ± 0.15 mm at the 0.05 level of significance. The dynamic accuracy ranged from 94.82 to 99.77%, and dynamic resolution ranged from 0.09 ± 0.26 to 0.61 ± 0.31 mm at the 0.05 level of significance. These values are comparable to those reported for a standard Vicon 524 (Oxford Metrics, Oxford, England) motion analysis system. The results support application of the lower cost Optitrack system for 3D kinematic assessment of upper and lower extremity motion during gait, assisted ambulation, and wheelchair mobility.
Motion Capture
Motion analysis
Cite
Citations (10)
An approach for model-free markerless motion capture of articulated kinematic structures is presented. This approach is centered our method for generating underlying nonlinear axes (or a skeleton curve) from the volume of an arbitrary rigid-body model. We describe the use of skeleton curves for deriving a kinematic model and motion (in the form of joint angles over time) from a captured volume sequence. Our motion capture method uses a skeleton curve, found in each frame of a volume sequence, to automatically determine kinematic postures. These postures are then aligned to determine a common kinematic model for the volume sequence. The derived kinematic model is then reapplied to each frame in the volume sequence to find the motion suited to this model. We demonstrate our method for several types of motion from synthetically generated volume sequences with arbitrary kinematic topology and human volume sequences captured from a set of multiple calibrated cameras.
Motion Capture
Sequence (biology)
Cite
Citations (87)
Structure from Motion
Motion field
Stereo imaging
Computer stereo vision
Cite
Citations (0)
The most recent models of depth cue combination assume that information provided by each cue is processed in isolation. Depth estimates are subsequently combined through a weighted average, where the weights are inversely proportional to the variance of each estimate (Modified Weak Fusion model; Landy et al., 1995, Vision Research, 35-3). These approaches ignore the covariance existing in real-world situations among 2D depth-cues. Specifically, in the case of a rigid transformation, disparity and velocity signals are linearly related to each other such that, if the stimulus is small enough, the ratio between velocities and disparities must be constant at any instant of time. In this study we investigated whether this relationship is utilized in visual processing of depth information. In two experiments (motion parallax and vertical rotation) observers viewed a 3D structure defined by a set of randomly distributed dots in a spherical volume. We asked observers to adjust the depth of a probe dot located at the center of this structure until it was perceived to be co-planar with two comparison dots. The ratio between the velocity and disparity values of the probe dot was kept constant during each adjustment but was varied in five experimental conditions. In only one condition this ratio coincided with the ratio of velocities and disparities of the dots in the structure. If motion and stereo signals are independently combined, velocity and stereo settings of the probe dot should fall on a straight line. On the other hand, if the visual system is sensitive to the co-variation of stereo and motion signals, we expect observers' adjustments to follow a specific non-linear pattern (Di Luca, Domini, Caudek, 2003, Perception, 32-Supplement). Our results are clearly compatible with this second prediction.
Parallax
Stereoscopic acuity
Constant (computer programming)
Cite
Citations (0)
Motion analysis
Cite
Citations (9)
Structure from Motion
Quarter-pixel motion
Cite
Citations (3)
The tracking and simulation of human motion are important tools for medical diagnoses and treatment. A micro detector with integrated micro electro-mechanical sensors, such as accelerometers and magnetometers, was used for motion tracking and online simulation. Models based on rotation of a single body and rotation of pairs of axes simplified the computations while producing outstanding visual movement characteristics for the human posture. A head motion experiment was also performed to measure and simulate dynamic head movements. The test further validates that the system can detect the attitude angle and the rotation rate of human motion to provide fast simulation of the motion.
Tracking (education)
Match moving
Tracking system
Cite
Citations (2)
Current theories of depth-cue combination postulate independent modules in the visual system for processing separate cues to depth. Further, the outputs of these modules are associated with weights based on the reliabilities of the depth estimates, as described by the modified weak fusion (MWF) model (Landy et al., 1995). In this study, the MWF model was tested by asking observers to provide depth judgments from (i) stereo-alone, (ii) motion-alone, and (iii) stereo and motion combined. The observers' task was to judge whether the apparent elongation of a horizontally oriented cylinder was more or less deep than an apparently circular cylinder (ACC) — see Johnston et al. (1994). The MWF model predicts that the mean estimate of observers' settings in the combined-cue condition will be a linear combination of the depth magnitudes from the stereo-alone and motion-alone conditions, each weighted by a reliability measure computed from the variances of observers' judgments in the two conditions. Our results do not conform to the predictions of the MWF model: perceived depth judgements were overestimated in the combined-cue and motion- alone conditions whereas stereo-alone judgements were veridical, despite the greater variance (less reliability) of the motion-alone condition. On the other hand, the MWF model predicts that perceived depth in the combined-cue condition should be closer to the depth estimate based on the more reliable cue (stereo, in our investigation). The present results are predicted by a new theory (Domini, Vuong, and Caudek; Di Luca, Domini, and Caudek ) which postulates that the visual system takes into account natural covariation of depth cues.
Cite
Citations (1)
With the rapid advancement of micro-sensor motion capture, human modeling and motion reconstruction in realtime have become more and more important. The human model must be accurate enough for representing motions but also simple to realize real-time application. In this paper, we build a human model for micro-sensor motion capture (MMocap) and reconstruct 3D human motion using data from MMocap in real-time. The human model is composed of bones and joints, driven by motion parameters from micro-sensor motion capture, resulting in the real-time 3D motion animation. The motion parameters include quaternion and position of each bone. Quaternions are used to represent orientation of bones. Positions are calculated from forward kinematics. The experimental results have shown that the proposed human model is of good fidelity and low delay for real-time micro-sensor data-driven motion capture.
Motion Capture
Position (finance)
Human motion
Cite
Citations (15)