Camera Calibration

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Camera Calibration
(Calibration Triangle and Wand are located inside both small and large mocap stage. Please DO NOT take those out of the room.)

Calibration Triangle and wand



Camera Calibration (room calibration or wand calibration) is an integral part of all modern motion capturing systems. The items shown in Figure 15 – Calibration Triangle and Figure 16 - Wand are the tools that are used in order to perform the room calibration. The purpose of the room calibration is to allow the Vision Processor to determine where each camera is located in 3D space (wand) and to show the system where the floor is, what direction is forward, and also a global scale value (triangle). The first time the system is started, all cameras will be located at the origin.

The room calibration process has four main steps and should take only a few minutes.

To get started first:

  • Click on the ‘Cameras’ tab in the display area.
  • Click on the ‘Stage Setup’ tab in the control area.
  • Click on the ‘Calibration Wizard…‘.
calibration wizard


























Step 1 – Lighting Settings:
First you will choose a lighting setting which makes the cameras practically black but the wand will show up as a white dot. The default values should be fine. When the ‘Next’ button is pressed the system captures a background image. It is important that when you click ‘next’, the wand or any moving/changing light is not visible by any camera. If it is, then calibration may not work correctly.

CameraCali001.PNG

Step 2 – Acquire Wand Points:
you will see at bottom image – Acquire Wand Points. This is where you will move the wand in the calibration space and the system can calibrate positions of the cameras.

  • Threshold – should not need to be modified. Threshold to filter bad samples is ( 0.2 – 1.0 ). The higher number allows for more difficult calibrations.
    1. Max ignore – the number of cameras that the system should allow not to calibrate.
  • Axis Length (cm) – the distance between the lights on the long arm of the Calibration Triangle displayed in Figure 15 – Calibration Triangle. This should not be changed.
  • Start Acquisition – start acquiring points
  • Solve – Calculate the quality and generate new calibrations for all cameras
  • Automatic – automatically solve as points are being acquired
  • Test – test the existing calibration – It will give you a quality value of your current calibration.
CameraCali002.PNG


The default settings do not need to be modified.

  • 1. Click on ‘Start Acquisition’
  • 2. Walk into the space and turn on the wand.
  • 3. Wave the wand in big circles. It is not necessary to move quickly. You should make sure that you move into the view of each camera and are at least a foot or more away from all cameras most of the time.
  • 4. When the system is finished the lights will flash.
    • a. If it is taking too long you can at any time press ‘solve’ to manually solve.
    • b. You should have between 500 and 800 points. If there are much more then there may be an issue. You should consult section 10.3 - Tracking & Calibration or read on.
  • 5. Figure 20 - Camera Calibration 3 – Calibration Result will appear where you can review your results.



If there are any missing cameras, the drop down will have the camera numbers of the missing cameras. These numbers start at ‘0’ and go to the number of required cameras. If there are any missing cameras please consult Troubleshooting section 10.2.9. If you would like to continue without calibrating the missing cameras, go back to the previous screen, put in a number for # Max. ignore and click solve again. The quality of the calibration should be in the high 90’s in order to be considered a working calibration. Generally, a calibration is considered good if it has a quality above 98.


Step 3 – Orientation and Scale:
Once the cameras have been calibrated, the system must have the floor and size calibration. Place the Calibration Triangle on the floor LEDs up with the short edge facing the back of the capture space. Make sure it is on with all 3 LEDs brightly lit. Place the corner of the Calibration Triangle in the center of the tracking space. This will be the ‘0,0’ position.

CameraCali003.PNG

Make sure that the Calibration Triangle is as square to the space as possible as you want the cut box / tracking limits to fit nicely within the tracking space. Now click ‘Acquire Origin’. The system should say ‘Success’. If it failed please move the Calibration Triangle slightly and try again. Press ‘Next’ once you receive ‘Success’.


Step 4 – Review:

CameraCali004.PNG

Now you have successfully calibrated Stage. You may view the calibration in this window to verify that it is reasonable. In this window you can use the same mouse controls as you would use in the normal 3D view or Core view. If you are not satisfied with the calibration you may click back and calibrate again. Otherwise, click Finish and you will be returned to the regular Stage Administration.