# Overview of nose-tail base detection

When you set an experiment for Nose-tail base detection, EthoVision XT analyzes the contour of the area detected as subject at each sample, and assigns Nose-point and Tail-base to two specific pixels of the contour. Furthermore, it determines the direction the animal is supposed to point to (Head direction).

Nose-tail base detection is optimized for rodents and for adult fish, depending on the method used.

Nose- and tail-base points

The two points are detected independently through one of two complex algorithms. The nose-point is found in all cases, except when the center-point is not found either. The tail-base may not be found in a few cases if detection is good.

Reliable tracking of nose and tail-base is limited by the size of the video image. You can mix four camera images like in the case of a group of PhenoTypers, with good results. Mixing 16 camera images makes the subjects too small for reliable nose and tail-base tracking.

Head direction

Once the nose-point has been found, two points are determined along the contour lying at a specific distance from the nose-point. The Head direction is the line dividing equally the angle formed by the center and those additional points.

important If you use Nose-tail tracking with two or more subjects per Arena, track from video file instead of live.