Camera Calibration in Motive | Scribe

    Camera Calibration in Motive

    • Zhongtian Wang |
    • 18 steps |
    • 43 seconds
      1
      This guide introduces steps on how to perform a Camera Calibration in Motive.\ \ It is necessary to perform a calibration under these circumstances: 1. First time setting up a system in a new location 2. Cameras have changed aim/focus OR been put in new location/bumped 3. Origin point/ground plane has been relocated 4. Tracking is inaccurate 5. General maintenance every 1-3 months
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      Change to the "Calibration" layout in the top right corner
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      Before calibrating, ensure Motive is set to "Passive" mode
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      Select all the cameras in the Devices tab. \ Make sure the IR Filter is on, Video Mode is set to Object, and Exposure/Gain are set properly.
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      To determine the appropriate brightness during wanding, start with an exposure of 500. Bring the wand out and walk around the space to test if all points are clearly visible to each sensor. If not, increase exposure by 500 and test. Repeat until the 3 points on the wand are clearly visible to all sensors.
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      In the Calibration panel on the right side, click "Clear Mask". This will clear all the existing masks.
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      Click "Mask Visible"
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      Masks work on a per-camera basis, which is a 2D view. It is useful for blocking unwanted IR sources, such as open doors and windows that lead to the outdoors, or exhaust from A/C or projectors that produce enough heat to generate IR. Masking them out will reduce IR interference and improve tracking performance.
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      Set Wand parameters: For a 1m wand, the length is 1000mm, center distance is 350mm.\ \ For a half meter wand, the length is 500mm, and the center distance is 175mm. For calibration type, refine calibration is only wanding, not setting ground plane. It should only be used when a camera position has changed, but the origin point has already been set and isn't changing.
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      Click " Start Wanding"
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      Wave the wand throughout the space (see note below on Wanding Techniques). If all 3 IR lights are seen at the same time by at least 2 cameras, a sample will be recorded.
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      Common wanding techniques include the "figure eight" (moving your arm in a large figure-eight, allowing the wand to twist around) and the "pizza slice" (holding the wand by one end and slicing back and forth, bulbs facing up). When wanding, try to get as complete coverage as possible. At the same time, avoid wanding in the same location multiple times because high sample count overlapping in the same location can create difficulty for the calibration process, leading to worse results. You can turn off the power to the wand to go across already wanded areas.
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      Sufficient sample count will vary across venue sizes and camera distance. Focus on increasing coverage within the camera's FOV: the goal is to fill the window as much as possible. The calibration shown in Step 8 is an example of good coverage. Below is an example of bad coverage.
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      Click on "Calculate" when wanding is complete. The software will then take some time to calculate the position of each camera, and will produce the result once done.
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      There will be 6 possible results: Poor/Fair: Redo as soon as possible, unless emergency with no time. Good/Great: Good enough, but should redo if able to. Excellent/Exceptional: Wonderful, ready to use. Under rare circumstances when the wanding is extremely poor, there won't be a result displayed.
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      You can also consult the Camera Summary tab on the bottom right corner, which has result bars showing what cameras are struggling. You can then decide to wand more or move the cameras. This can help you make informed decision on how to redo your calibrations. This shows if cameras need more samples, or if the 2D coverage of the sensor needs to be improved.
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      Click on "Apply" from the result dialogue, and you will be directed to the Ground Plane setup tab. Once the calibration result is applied, the cameras understand their relationship to each other, but not to the ground. This is where the ground plane comes in.
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      Vertical offset is 90mm for the ground plane comes with the 1m wand, and 45mm for the half meter wand. The vertical offset should only be set to 90/45mm **if the ground plane is set up on the ground level**. Sometimes the ground or Z height is higher or lower than the level the ground plane can be set at. In those cases, the vertical offset needs to be measured instead
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      Place the Ground Plane at the origin point drawn in WYSIWYG (or another 3rd-party software), with the positive X and Y directions matching those in WYSIWYG
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      Blacktrax uses the following coordinate system: X is width (left/right in topdown view), Y is depth (up/down in topdown view), and Z is height