Body angle

Definition

The angle formed by the prolongation of the segment joining the tail-base and the center-point, and the segment joining the center-point and the nose-point, calculated at the current sample.

 

Range

Absolute Body angle ranges from 0º to 180º. Relative Body angle ranges from -180º to +180º.

0º occurs when the nose point, center point and tail base point are aligned. Values around ±180º are only hypothetical, because they would imply that the animal is completely curled up in such a way that the nose points to the tail base. Values higher than 100º often occur with wrong detection of the body points.

How to specify Body angle

1.Click the Add button next to Body angle.

2.In the Body Angle tab, specify whether you want to calculate:

▪Absolute angle: The unsigned angle.

▪Relative angle: The signed angle. It is negative when the body is bent to the right (clockwise); positive when the body is bent to the left (counterclockwise).

 

3.Complete the procedure to add the variable. See Calculate statistics: procedure.

Note

When the nose-point and the tail-base point are swapped, and these are not properly corrected in the Track Editor, the value of relative body angle is opposite to what it should be. For example, if the actual body angle is +10º, EthoVision XT gives -10º. However, absolute angle remains correct. Therefore, if your track contains nose-tail base swaps, either correct them in the Track Editor, or use Absolute angle.