Tangent vector

$$\vec{\tau}(s) = \frac{d\gamma}{ds}(s)$$

$\vec{\tau}$ depends on orientation, and is a unit vector:

$$\left\vert\frac{d\gamma}{ds}\right\vert = \left\vert\frac{d\gamm... ...t\vert\frac{d\gamma}{dt}\right\vert/\left\vert\frac{d\gamma}{dt}\right\vert = 1$$