Calibrating

Standard calibration

In this method, all cameras are calibrated simultaneously.

  1. Before continuing, ensure that you have configured your PPT cameras to optimal sensitivity and thresholds, and that your workspace lighting is ready for data collection (e.g., outside windows blocked, warm lights off).

  3. Turn off all of your PPT markers.

  5. Turn on the PPT calibration rig and place it in the center of your workspace. Orient the calibration rig so that the +X and +Z axis markers are aligned in the directions that you desire for PPT's coordinate system. PPT north is defined as the direction of the +Z axis.

  7. Try to keep the rig as close to the center of each camera's field-of-view as possible. Avoid placing the calibration rig markers at extreme edges of a camera's view. Use the Cameras panel to view all of the cameras simultaneously.

  9. Click the Calibrate tab in the main viewport. This will launch the calibration wizard.

  1. Find the Calibration Rig Size options and select the proper calibration rig size. The size is defined by the distance between the adjacent IR LEDs. In general, a system usually comes with a calibration rig which has the default size (57cm).

  1. For a standard calibration, all cameras should be reset to Uncalibrated (as indicated by the red icon next to each camera). If this is not the case, click the Reset button before proceeding.

  1. Click the Calibrate button at the top of the window. Each of the camera's four indicator lights will turn green for each flash of the PPT calibration rig. If any camera fails to light up all green, then there was a problem with that camera seeing all four markers of the PPT calibration rig. Use the Cameras panel to re-examine that camera.

  3. If all cameras calibrated successfully, you'll receive a quality score. Scores of 99.3 and above are acceptable.

Low Calibration Score

Possible causes for a low calibration score are:

  • Deformed calibration rig

  • The intrisic calibration of one or more cameras is broken. This will occur if the camera lense has been turned. To troubleshoot, remove one camera at a time, recalibrate and see if the score improves.

A subpar calibration will result in jumpy tracking when a marker gets occluded.

Chained calibration

In this method, cameras are calibrated in stages. Use this method for a physical workspace where not all cameras can see the calibration rig simultaneously (e.g., the room is L-shaped).

  1. Follow steps 1 - 4 above.

  3. If you're starting a new chained calibration, click the Reset button to clear all previous data.

  5. Click the Calibrate button at the top of the window. Each of the camera's four indicator lights will turn green for each flash of the PPT calibration rig.

  7. Cameras that are fully calibrated are now indicated with the green checkmark icon. Cameras that show a yellow icon indicate that the camera saw all four makers on the calibration rig but it cannot yet chain due to lack of data from a neighboring (connecting) camera. Cameras that show a red icon indicate cameras that saw less than four markers on the calibration rig.

  9. Move the calibration rig enough so that some or all those cameras indicated as red can now fully see the calibration rig.

  11. Once all cameras are calibrated, you'll receive a quality score. Good scores are above 99.3.

NOTE about chaining

Chaining adds error to the calibration. Use as few calibration snapshots as possible, typically this is done by "sweeping" the calibration rig from one end of the space to the other. Try to have as much overlap between cameras between snapshots. If you suspect a camera calibrated but may contain poor measurements (e.g., the rig was at the extreme edge of the camera's view), you can easily right click on the camera to mark it as uncalibrated, and then redo it.