In ICE, we often work with point or particle positions, and these positions are **3D Vectors**.

Now, in general, a vector is something that has both value and direction (for example, any cyclist knows that the wind has both a magnitude and a direction, and together they **really **define the wind π

When you’re working with point/particle positions, you’re really working with **position vectors** that specify a unique position in space. You’re not really interested in the magnitude of the vector, just the head and tail of the vector.

For any position vector, the **tail **is the origin: the point (0, 0, 0).

The **head **of the vector is the position in space.

When you’re working with position vectors in ICE, it’s important to understand what coordinate system you are working in, because that determines the origin. For example, here’s two different position vectors for the same point: