12.2. Calibration

In general, the cameras should be calibrated every time they have not been used for a while. If you can be sure that the cameras have not been moved (accidentally), calibration should not be necessary (e.g. resuming experiments on the next day).

12.2.1. L-Frame Orientation & Position

We align the L-Frame with the x- and y-axis of the tank. The long arm axis aligns with the x-axis and the short arm with the y-axis.

It is a good idea to align the L-frame with one of the tags. That way, you can look up the (approximate) position of the tag.

../_images/l_frame_in_tank.jpg

Fig. 12.1 L-Frame position in tank.

12.2.2. Calibration Settings

Setting the orientation

Before you calibrate, you should set the L-Frame orientation. Changing this afterwards is a pain.

In the settings, under Input Devices - Camera System - Calibration, set the coordinate system orientation, set the coordinate frame orientaiton.

  • Axis pointing upwards: Positive z-axis (should be default)

  • Long arm axis: positive x-axis

../_images/calibration_orientation.png

Setting the translation

After you have successfully calibrated, you can translate the origin of the original coordinate system to be aligned with our definition in ROS.

../_images/calibration_translation.png

12.2.3. Calibration Results

An average residual under 1mm is desirable.

Attention

Remember to remove the L-Frame from the tank after finishing the calibration. Unfortunately, the markers are not waterproof…