Set up the volume

After you have completed a wand wave (see Perform a wand wave), the next step is to set the volume origin (see Set the volume origin).

Depending on your capture environment (for example, if your volume floor is not perfectly level), you may then need to set the floor plane. To further help with setting up your system, you may also want to set the floor grid and/or autonumber the cameras.

The following topics describe how to set up the volume.

Set the volume origin

After you have captured a wand wave (see Perform 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, in the Workspace, change the view to 3D View.

   

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 View).

   

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

3. In the Camera Calibration panel, to the right of Wand Wave, display the advanced parameters and 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. In the Volume Setup section, 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 View, ensure that in the View Filters options, Cameras is selected.

   

   
   In the 3D View, 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. In the Camera Calibration panel, go to the Volume Setup section, display Advanced Parameters and in the Set Floor Plane section, click Start Set Floor Plane.
   The button displays Set Floor Plane.

5. After a few seconds, click Set Floor Plane.
   In the 3D View, 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.

   

   
   

   Tip
   To more accurately visualize the size of your volume in Evoke, you can change the size and shape of the floor grid. To do this, in the Camera Calibration panel, go to the Volume Setup section, ensure the Advanced options are displayed, and in the Set Floor Grid section, change the values (in mm) to produce the required result.

Adjust the Set Floor Plane settings

When setting the floor plane, Evoke uses the center of all markers it has identified as being in the same plane. As the center of the marker is actually above the ground, you will need to specify an offset or else your floor plane (and Global Origin) may be higher than desired. To set the floor plane accurately, in the Camera Calibration panel, go to the Volume Setup section, ensure the Advanced options are displayed, and in the Set Floor Plane section, change the Height offset 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.

Set the floor grid

To more accurately visualize the dimensions of your volume in Evoke, you can change the size and shape of the floor grid.

To do this:

1. In the Camera Calibration panel, to the right of Volume Setup, ensure Advanced Parameters is selected.

2. Expand the Set Floor Gridsection and change the values (in mm) to produce the required result.
3. Click Set Floor Grid.

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, in the System panel, ensure that you can see the list of Vicon cameras.

3. In the Camera Calibration panel, go to the Volume Setup section, ensure advanced parameters are displayed and 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.