Check camera positions

Evoke enables you to check whether any cameras have moved by comparing the current camera positions with a snapshot (baseline) of camera LEDs from the previous Evoke session. It also provides information on when a re-calibration is required.

When you first start using your Origin system, it is advisable to run a calibration assessment daily, before use. When you have become familiar with how much the rig shifts or cameras get knocked, you may be able to reduce the frequency of this check.

Generate baseline

To generate information on the cameras' current positions:

• On the Calibration Assessment tab, click Generate Baseline.Blue marks are displayed next to most cameras. Each mark represents the LEDs of the other cameras that can be seen by the camera.

  

Assess current calibration

After you have generated a baseline from which the camera positions can be assessed, you check for camera movement. To do this:

• On the Calibration Assessment tab, click Assess Calibration.

  

  On the Calibration Assessment tab,most or all of the blue marks turn green.

Green marks indicate that the camera position is unchanged since the last calibration.

Red marks indicate that something has changed in the calibration, either due to a bump or knock, or because of environmental drift.

Depending on whether you have Enable Auto Bump Healing selected (the default), you may need to take action to correct any changes.

• Enable automatic recovery of moved cameras
• Manually recover moved cameras

Enable automatic recovery of moved cameras

When you run Assess Calibration, Evoke may indicate that a camera has been moved. If a camera has been bumped enough to move its position, the move is detected, so the LEDs flash red on the camera, and the System pane and Cameras view display a bump icon to the right of the camera name.

To enable the recovery of a moved camera:

1. On the Processing tab, go to the Camera Healing section and make sure Enable Auto Bump Healing is selected (its default setting).
   

   

2. In the volume, have someone wave two of the Pulsars used to set the floor plane in front of the camera until its status light turns blue (or magenta if selected).
3. To generate a new baseline, on the Calibration Assessment tab click Generate Baseline. This creates a baseline that contains the updated information about the camera positions.

For more information:

• For Vicon systems that use cameras with built-in strobes (such as Vero or Vantage cameras), see Automatic recovery for systems with strobed cameras.
• If Auto Bump Healing doesn't seem to be recognizing or recovering cameras that have moved, see Understand automatic recovery of moved cameras.

Automatic recovery for systems with strobed cameras

Auto Bump Healing is turned on by default.

The option for generating online masks is disabled by default. To enable this option, which is recommended for use with Vicon systems that include cameras with built-in strobes (such as Vero or Vantage cameras):

1. In the Processing panel, ensure the Advanced properties are displayed.
2. In the Camera Healing section, select Generate Online Masks.

   

In some situations, you may need to deactivate Auto Bump Healing, for example, for systems where there is no overhead for the additional processing required, and in some cases where large numbers of centroids are generated from non-object sources (eg, reflections from participants' clothing). In this latter case, some other mitigation is often available (eg, by reducing the strobe intensity of the cameras), but in extreme cases it may be better to deactivate Auto Bump Healing.

To turn off Auto Bump Healing, on the Processing tab, go to the Camera Healing section and clear Enable Auto Bump Healing.

Understand automatic recovery of moved cameras

When Enable Auto Bump Healing is selected, the system detects cameras that have stopped contributing centroids to the tracked objects in the volume if:

• The system health connection score for the camera is below 25% (to check this, at the top of the Cameras view, hover the mouse pointer over the Connection score icon ).

• Enough centroids are visible to this camera.

If these criteria are met, the system attempts to bump-heal (recover the position of) the camera. It collects data for a short time and if there is sufficient coverage in the cameras view and the system can find a solution, it applies a new calibration for this camera. This causes the system calibration file to be re-saved to the following default location:

C:\ProgramData\Vicon\Calibrations\LatestCalibration.xcp

For successful automatic recovery of moved cameras, ensure that your system meets the following criteria:

• The cameras’ internal parameters (focal length, radial distortion, etc) do not change.
• The cameras have achieved a stable operating temperature before calibration and before starting an experience.
• Objects are being tracked by a majority cameras. The easiest way to check this is to select all cameras (or no cameras), look in the Cameras view and in View Filters ensure Centroids is selected. Check that the centroids are green and that no calibration warning icons are displayed.
• The bumped camera(s) can see objects and they are generating 2D tracks.
• No unmasked camera strobes or reflective objects are present in the system. These may cause the system health of the camera to remain low and to trigger further recalibration.

If you need further information about which camera has moved, what may be causing an issue and whether it has been successfully recovered, check the Log (if it isn't displayed, on the View menu, select Log). The errors, warnings and messages will look similar to this:

In the above examples, the camera's Device ID is highlighted.

To find a camera's Device ID, on the System tab, select the camera, click Show Advanced in the General section, scroll to Device ID.

Manually recover moved cameras

When you run Assess Calibration, Evoke may indicate that a camera has been moved. On the moved camera, the LEDs to flash red and on the System tab and Cameras view, the bump icon is displayed to the right of the camera name.

If Enable Auto Bump Healing (see above) is not selected, you can recover a moved camera by using Evoke's Recover Camera Position option.

To recover a moved camera:

1. In the Tools pane, on the Camera Calibration tab, click Start Recover Camera Position and in the volume, wave two of the Pulsars in front of the affected camera.
   In the 3D Scene and Cameras view, orange trails are displayed as the system determines the offset between the camera and the rest of the calibration.
2. When enough of the view has been covered (indicated by orange trails that thickly cover the affected camera view), click Recover Camera Position.
3. In the Cameras view, zoom in and check that the centroids are now green, and the red icon to the right of the camera names have gone.
4. To generate a new baseline, on the Calibration Assessment tab click Generate Baseline. This creates a baseline that contains the updated information about the camera positions.

Compensate for camera calibration drift

When small changes occur in the pose or internal parameters of the camera (eg, through temperature changes that cause the thermal expansion of the rig), this can cause centroids to fail to be labeled as part of a tracked object.

The Auto Bias Handling feature attempts to compute the camera calibration biases and increase the slack used when deciding whether a centroid should correspond to a model point in order to compensate.

To turn Auto Bias Handling on or off:

1. In the Processing panel, ensure the Advanced options are displayed.
2. Go to the Camera Healing section and select or clear Enable Bias Handling. This option is selected by default.

The bias correction does consume additional CPU resources but is unlikely to affect experience latency for standard tracking.

This parameter can be thought of as an automated version of the Environmental Drift Tolerance parameter for reconstructions, but dedicated to object tracking. Note that if objects are struggling to boot, you may also need to increase the Environmental Drift Tolerance.