Best practices

Overall

01
Ensure you are connected to a stable Internet connection. Video upload may fail with a poor connection.
02
Do not move cameras once you've passed the calibration step. If you accidentally moved a camera, start a new session.
03
The checkerboard is only used for calibrating the cameras, you can remove it after successfully completing the calibration step.

Camera setup

  • The camera on the back of the iOS device, rear-facing camera, is the one used for recording.
  • Position the cameras to avoid segment occlusions.
  • Avoid people in the background, although OpenCap is built to handle this.
  • Avoid having the participant exit and re-enter the capture volume.
  • At least two cameras need to see every body segment at all times during the movement. Two cameras is sufficient for many tasks, but tasks where segments get occluded may benefit from an additional front-facing camera.
  • For a two-camera setup, cameras at 30-45° off of the line facing forward from the participant is typically best. Pure sagittal views do not work well due to limb occlusion.
  • We recommend watching the participant perform the task of interest in each camera before calibration, to ensure that they remain within the field of view.

Camera calibration

  • Environment
    • Record in a well-lit environment.
    • If recording outdoors and there is direct sun on the checkerboard, you may want to shade it before calibrating.
  • Checkerboard dimensions
    • Use a checkerboard on at least A4 paper with squares at least 35mm. We recommend printing this board.
    • Ensure that the checkerboard has a white border around all sides.
    • Verify the dimensions of the checkerboard’s squares after printing.
    • The number of columns and rows that should be entered in the web application is the number of black-to-black corners, not the number of squares in the columns or rows.
  • Checkerboard position
    • The checkerboard should be visible by all cameras.
    • The checkerboard should be standing perpendicular to the ground, with its long edge parallel to the ground.
    • The line pointing out of the checkerboard should bisect the camera arc.
    • The checkerboard should be within less than 5m from the cameras.
    • The line pointing out of the checkerboard should not point straight at one of the cameras. Move the board up, down, right, or left to avoid this.
    • The checkerboard should be at the center of your desired capture volume, as close as possible to the cameras, while being visible by all cameras.

Data collection

  • Tight clothing that contrasts with a simple background and shoes that contrast with the floor and with the pants is helpful.
  • Start recording at least 1s before the participant begins the movement.
  • For treadmill gait or fairly static movements (e.g., postural sway assessment), have the participant punch one hand in the air above their shoulders and bring it back down at some point during the trial. This facilitates camera synchronization.
  • Colored dots next to trial names indicates the status of the trial: green (successfully processed), orange (being processed), red (error in processing). You may want to re-collect trials with a red-dot. Download data only when all dots have turned green (or red). Click on red dots to get insights into what went wrong.
  • You may collect data on another participant without re-calibrating the cameras by pressing "New session same setup".