Skeleton is incomplete

Explanation

In general, the 3D skeleton appears to be incomplete when one independent part of the kinematic chain cannot be tracked. The body parts that are able to disappear will depend on the joint constraints you have selected in the Analysis section of the Preferences window, and the cause of their disappearance can vary.

For example, when Enable Free Arms is not selected, the shoulder joint is modelled with 3 degrees of freedom (DOF), allowing full rotational freedom but no translation of the upper arm relative to the torso. Therefore, if one of the arms cannot be tracked, then the entire left arm + torso + right arm chain will disappear. However, if Enable Free Arms is selected the shoulder joint is modelled with 6 DOF, allowing the arms to be tracked independently of the torso. This allows any of the left arm/torso/right arm segments to be tracked, even if one of the other segments cannot be tracked.

There are several reasons why a body segment may disappear in a processed movement trial:

1. The Smoothing Frequency is set too low.

If the Smoothing Frequency is set too low, it is possible for the moving body part(s) to be detected as an outlier and excluded from the tracking. This typically occurs when the movement is very fast and the GCVSPL Cutoff Frequency is set relatively low.

1. The body segment is not sufficiently visible to be tracked reliably.

If the body segment is occluded or otherwise difficult to discern in the videos due to poor lighting, dark clothing, a challenging pose, or other factors, it may not be possible to track the segment reliably and it will disappear.

Possible Solutions

Some possible solutions for incomplete skeleton tracking are as follows:

1. Increase the Smoothing Frequency.

If the cause of the incomplete skeleton is a low Smoothing Frequency resulting in the body segment being detected as an outlier, try increasing the Smoothing Frequency to allow the movement to be tracked. After adjusting the Smoothing Frequency in the Preferences window, you only need to run the Solve Skeleton analysis step to view the updated pose results.

1. Use the Enhance Videos tool to improve the video quality.

If the videos are too dark or not properly white-balanced, they may be improved using the Enhance Videos tool. This can improve the visibility of body segments and improve tracking quality. After adjusting these settings, you will need to use the Run Analysis button to perform all analysis steps.

1. Improve the quality of the data recorded by your camera system.

If the data quality is insufficient to be able to clearly see all body segments, try improving the quality of the data collected by your camera system. You may need to make adjustments such as increasing the amount of ambient light, increasing the camera resolution, selecting appropriate frame rate and exposure settings, or moving the cameras closer to the participant to capture them with higher resolution.