Calibrate the floor plane

To ensure that your coordinate system is accurately aligned with the floor of the capture volume, which is particularly useful if the floor is uneven, you can adjust the position of the floor plane using markers in the volume to automatically define it.

To calibrate the floor plane:

1. Complete the camera calibration procedure (see Calibrate Vicon cameras) and set the origin (see Set the volume origin).
2. Turn off the calibration object or remove it from the volume.
3. Scatter a quantity of the same size Vicon markers across the floor of your capture volume. If you want Vicon Nexus to automatically recognize these markers as floor plane markers, ensure that they outnumber any other groups of markers (e.g, markers on a wand or markers that were used to focus cameras, etc).
4. In the System Preparation Tools pane, expand the Set Volume Origin section, click Show Advanced, and ensure that the options relating to Set Floor Plane are as required:
   
   • Auto detect: Markers are automatically detected, based on the marker group that defines the plane with the most markers. (If, when you click Auto detect, the wrong markers are selected in the 3D Perspective view, you can add or remove markers in the volume until selection is as required.) To ensure that the tolerance setting (in mm), which specifies the height of the group of markers that define the floor plane, is as required, click the drop-down arrow next to Auto Detect, and set the tolerance to a value that prevents a large variance in height (2mm is often enough).
   • Start: Enables you to manually select the markers that will determine the floor plane by clicking the required markers in the 3D Perspective view.
   • Offset: Select the check box and set the amount (in mm) by which to adjust the floor plane (default is zero) in X Y and Z planes. Because Nexus finds the centers of the markers, set a Z-offset that accounts for the size of the markers plus their bases (for example, for 14mm markers on 2mm bases, the Z-offset is -9mm).
5. If you clicked Start, when you have selected the required markers, click the Stop button. In the 3D Perspective view 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. The latest calibration (.xcp) file is updated. This calibration file is automatically copied to every subsequent trial captured.

Your Vicon cameras are now calibrated and ready to capture data.