Troubleshooting

Camera calibration

Make sure you follow the instructions in best practices.
Ensure all of your phones are paired to the session. The phone app will alert you that the phone has been paired after scanning the QR code. Ensure that there is no red warning on the iOS device screen indicating that the phone is not connected to the server. Connect to more reliable internet if it is disconnected.
Potential causes for a failed calibration:
Checkerboard too far from cameras. Printed board should be less than 5m away.
Wrong number of columns or rows. Make sure you count black-to-black corners.
Too bright of an environment (e.g., direct sunlight). Shade the checkerboard.
Too dark of an environment. Add some light to the checkerboard.
Checkerboard not mounted to something flat.
Checkerboard not fully visible by all cameras. Verify that it is in the field of view of each camera.
Checkerboard at too acute of an angle to the cameras. Bring the cameras within +/- 60° from the line perpendicular to the checkerboard.
Anything else? Contact us, we can dig in.

Neutral pose

Potential causes for a failed neutral pose:
Participant moving. Have the participant stand still until the message tells you they can relax
Bad camera calibration, try re-calibrating.
Participant not fully visible by at least 2 cameras. Verify field of view of all cameras.
Cameras not well positioned. Position cameras such as to capture both sides of the participant and limit occlusion.
Checkerboard not perpendicular to the floor during camera calibration. Start a new session and make sure the checkerboard is perpendicular to the floor during camera calibration.
Anything else? Contact us, we can dig in.
Model has inaccurate limb lengths or bad kinematics during dynamic trials
Calibration issue: if the line pointing out of the calibration board points directly at one of your cameras (i.e., the camera looks at the checkerboard straight on), you can have a bad calibration. Re-calibrate with the calibration board repositioned to avoid this.
Participant in the wrong pose. Have the participant stand in the pose shown in the web app.

Dynamic trials

Potential cause of a trial trimmed too short:
Camera fields of view are not sufficiently overlapping. Re-position cameras so at least 2 cameras can see the participant during the desired motion. If the participant only enters the capture volume for <2 seconds, the trials may fail.
Potential cause of inaccurate kinematics:
Videos not synchronized: Have the participant punch one hand in the air above their shoulder, then bring it back down at any point in the trial to synchronize the cameras. This is especially helpful for treadmill gait and activities that are fairly static (e.g., balance assessments).
Segment occlusion: Re-position cameras so each segment is seen by at least 2 cameras at all times.
Poor contrast between adjascent items of the participants clothing or poor contrast with the background. Wearing shoes that are a different color from the pants and from the floor is especially helpful. A simpler background will improve pose detection.
Bad camera calibration. Try re-calibrating.
Checkerboard not perpendicular to the floor during camera calibration. Start a new session and make sure the checkerboard is perpendicular to the floor during camera calibration.
Participant too far from cameras. If they can come closer to the camera, this will help. If it is important that they are far from the cameras (e.g., running), we may be able to reprocess the data with a higher resolution algorithm. Contact us if you think this may be the case.
Camera angles too close together: 40-90° separation of cameras, symmetric around the direction the subject is moving along is good for many tasks. Camera positions may need to be changed to avoid segment occlusion.
Anything else? Contact us, we can dig in.