# Modify the coordinate system of the arena

Aim

To have the coordinates system different from the default one. For example:

▪You want to export the real-world coordinates and you want these coordinates expressed relative to a point of reference in the real world that is not in the middle of your image.

▪You want the dependent variables that use angle (that is, Head direction, heading, Meander, Turn angle), to be expressed relative to a reference line that is different from the default one (horizontal and pointing to the right). For example, you have an external cue to the north-east of your arena and you want to express the animal's orientation relative to this cue. In this case, you rotate the Calibration Axes so the x-axis points towards the cue.

Use the Calibration Axes object to specify the orientation of the real-world coordinate system and to specify the real-world coordinates for one pixel point.

To modify the coordinates system

1.Click the Create Calibration Axes button at the bottom of the Arenas and Zones section.

2. optional In the Calibration Coordinate System window, type in the real-world origin of the x-axis Origin X and of the y-axis Origin Y relative to the current position of the origin on your screen. Do this if you know the origin of the coordinate system is outside the background image. Alternatively, skip this step and go to the next.

example If you type 10 (cm) for Origin X, it means the origin [0,0] of your calibration system is shifted 10 cm to the left relative to the center of the video image.

3.Click and drag the Calibration Axes object to re-position the axes origin.

To flip the y-axis of the Calibration Axes object, double-click the Calibration Axes object and select Flipped Y-axis. Move the Rotation mode arrow to rotate the calibration axes.

To return to the default coordinates system

Select the Calibration Axes object and press Delete.