Calibrate cameras

When you first connect up your Vicon system and start Vicon Evoke, notice that on the System tab and in the Cameras view, icons give you feedback on the current status of the cameras. The cyan icon indicates that although the cameras are connected, they are not yet calibrated.

To calibrate your Vicon cameras, complete these procedures in order listed in this guide.

Evoke also enables you to calibrate or re-calibrate a single camera, without having to re-calibrate the whole system. To find out how to do this, see Calibrate a single camera.

Mask cameras

You mask cameras during camera calibration to eliminate any unwanted reflections in the capture volume, so that they are not mistaken for markers by the cameras. Before you start masking, you can see these reflections represented by light pixels in the Cameras view. During masking, blue pixels are drawn in the Cameras view, enabling you to see how much of the view is masked.

To automatically mask reflections:

1. Ensure you have disabled or turned off any Pulsars and props that use active markers. Note that, to start masking, at least one camera must be contributing data.
2. In the Workspace, select the Cameras view.

   

3. On the System tab, select all the cameras (SHIFT+click or drag or right-click and then click Select All Cameras).

4. On the Camera Calibration tab, click Start Masking (All).

   The button displays Stop Masking and at the top of the workspace, Auto Mask Active and a flashing red circle is displayed.

   On the cameras, the status lights turn cyan while auto masking is in progress.

   Evoke starts tracking the data visible to each of the connected cameras. Any camera masks created are displayed as blue cells in the Cameras views for affected cameras. If no data is visible to a particular camera, Evoke does not create any masks for it.

5. After about 5–10 seconds, click Stop Masking.
6. In the Cameras view for each camera, ensure that any unwanted reflections are eliminated. (Each view should either be completely blank or should contain some blue pixels.)

If the automatic camera masking that is described above does not eliminate all the unwanted reflections, you can manually remove any remaining reflections as follows.

To define camera masks manually:

1. In the System tree or 3D Scene, select a single camera.
2. On the Camera Calibration tab, ensure the advanced options are displayed (if necessary, click Show Advanced at the top right).
3. To begin editing the selected camera mask, on the Camera Calibration tab, click Start Manual Mask Paint.
4. In the Cameras view:
   • Alt+drag to select a mask area

     

   • Press E to add the current selection to the mask

     

   • Press R to remove the current selection

     

5. To apply the changes, click Stop Manual Mask Paint.
   To revert to the original mask, click Cancel.

You can now perform a wand wave.

Wand wave

During camera calibration, after you have masked any reflections, you calibrate the cameras by waving a wand (the calibration device) throughout the volume to enable the cameras to capture movements over the whole area.

To perform a wand wave:

1. Ensure the Wand is in Continuous mode.
2. In Evoke, click Start Wave (All).
   The button displays Stop Wave and in the menu bar, the text Camera Calibration Active is displayed, next to a flashing red circle.

3. Have someone wave the wand throughout the capture volume, covering depth as well as height, while you watch the Cameras views for all cameras to ensure you get full coverage. Ensure that the markers (LEDs) on the wand remain visible to all the cameras as much as possible while the wand is moved throughout the volume.

   As an indication of the age of the wand detection, to help you see where the wand is being waved and getting detections, the display in the each view changes from orange to blue.

   

   On the Camera Calibration tab, notice that the Wand Count column changes from red to green as sufficient data per camera is captured. This helps you concentrate on waving the wand for cameras that need more data.

   Tip: By default, camera calibration stops automatically when each camera has seen enough of the wand to ensure calibration. To adjust this or turn it off, at the top right of the Camera Calibration tab, first click Show Advanced. To adjust the amount of data needed before the camera calibration stops, in the Calibration Wave section, change the value of Auto Stop Minimum Wands. To turn off the automatic stop, clear the Auto Stop check box. Note that if you do this, the Wand Count column does not change color, and you will have to estimate when sufficient data has been captured.

4. After the wand wave has stopped, in the Image Error column, in addition to displaying the values, Evoke grades the status of each camera between red (poor) and green (excellent), depending on how much the cameras see the wand.

   

   In the volume, thestatus lights on the Viper cameras turn magenta and blink during calibration, becoming green and then blue when fully calibrated.

Set the volume origin

After you have captured a wand wave, you set the volume origin and axes so the cameras and volume in Evoke reflect the actual positions of the cameras in relation to the volume, as well as to each other.

1. To enable you to see the axes in relation to the volume, on the Workspace tab, change the view to 3D Scene.

   

2. Place the calibration device on the volume floor in the position you want the volume origin to be and in the orientation you want the axes to be (reflected in the axes displayed in the 3D Scene view).

   

   • Z axis: blue line
   • X axis: red line
   • Y axis: green line

3. At the top of the Camera Calibration tab, in the Wand list, ensure the appropriate Active Wand is selected (normally Active Wand v2).

   Tip: Using a Vicon Active Wand enables you to set up your volume coordinate system quickly and easily. However, using a larger calibration object (for example, markers embedded in the volume floor and wall) can improve calibration stability and consistency over time, particularly in larger volumes. For more information, see Create a custom calibration object.

4. Click Start Set Origin.

   The button displays Set Origin and is unavailable until Evoke has enough data to set the origin .

   If you need more information about why the button is unavailable, hover the mouse pointer over the button to view its tooltip. For more information, see About collecting frames .

5. Click Set Origin.

6. In the 3D Scene, ensure that in the View Filters options, Cameras is selected.

   

   In the 3D Scene, Perspective view, all of the cameras shift as a group, so the origin of the volume is aligned with the wand.

   

About collecting frames

If Evoke detects an issue with setting the origin, the tooltip for the Set Origin button displays the following information in the format 'Collecting frames (reason origin can't be set)' so that you can take the appropriate action:

Set the floor plane

The final stage in calibrating your Vicon cameras is to set the floor plane, using Pulsars in the volume to automatically define it.

The position of the virtual floor that is derived during setting the origin is extrapolated from the position of the wand in relation to floor of the volume. As the wand is a small object compared with the size of the volume, any slight discrepancy from the wand being level has a large effect over the rest of the volume when you set the origin. To account for any discrepancy, you set a floor plane, which takes a much larger area into account, so that the virtual floor lines up correctly with the actual floor plane.

To set the floor plane:

1. Ensure you have completed the rest of the camera calibration procedure and set the origin (see Set the volume origin).
2. Turn off the wand or remove it from the volume.
3. Place a minimum of four Pulsar clusters across the volume floor.
   (If you need to change the default 7 mm floor plane setting (the setting for Pulsars is normally 14 mm), see Adjust the Set Floor Plane settings.)
4. On the Camera Calibration tab, click Start Set Floor Plane.
   The button displays Set Floor Plane.

5. After a few seconds, click Set Floor Plane.

   In the 3D Scene, ensure that in the View Filters options, Cameras is selected.

   In the Perspective view, notice that the cameras shift as a group slightly along one or more rotation axes to better reflect an average of the markers scattered across the floor, taking into account any offsets that you specified.

   

Adjust the Set Floor Plane settings

If you need to change the default floor plane setting, to enable you to set the floor plane accurately, click Show Advanced and change the Height offset value to an appropriate value.

The Height offset is the amount (in mm) by which to adjust the floor plane (the default is 7 mm). Because Evoke finds the centers of the Pulsars, set a Height offset that accounts for the size of the Pulsars (normally 14 mm). If the Pulsars include a base, take this into account in your calculations.

Autonumber cameras

The Auto Number Cameras feature numbers the currently connected Vicon cameras in ascending order, according to their position in the volume. You may want to do this after you calibrate your Vicon system, so that your cameras are logically numbered before you begin tracking.

Automatic numbering starts with the camera that is furthest from the volume origin. The cameras are then numbered in a clockwise direction around the volume. If your cameras are positioned at different levels, the cameras in the level that contains the most cameras are numbered first.

To automatically number Vicon cameras:

1. Ensure that the cameras are positioned as required, and that you have calibrated the cameras and set the volume origin.
2. To enable you to check the camera numbering for all cameras, on the System tab, ensure that you can see the list of Vicon cameras.

3. On the Camera Calibration tab, in the Auto Number Cameras section, click Auto Number Cameras.

   The cameras are automatically numbered in ascending order, according to their position in the volume.

4. In the volume, check that the cameras are now numbered as required.