Unitization

Unitization is the process of scaling an element of a projective geometric algebra so that its weight norm becomes the antiscalar $$\large\unicode{x1D7D9}$$. An element that has a weight norm of $$\large\unicode{x1D7D9}$$ is said to be unitized.

An element $$\mathbf u$$ is unitized by calculating

$$\mathbf{\hat u} = \dfrac{\mathbf u}{\left\Vert\mathbf u\right\Vert_\unicode["segoe ui symbol"]{x25CB}} = \dfrac{\mathbf u}{\sqrt{\mathbf u \mathbin{\unicode["segoe ui symbol"]{x2218}} \mathbf u}}$$ .

In general, an element is unitized when the combined magnitude of all of its components having a factor of $$\mathbf e_4$$ is unity. That is, the components of the element that extend into the projective fourth dimension collectively have a size of one.

The following table lists the unitization conditions for the main types in the 4D rigid geometric algebra $$\mathcal G_{3,0,1}$$.

Type	Definition	Unitization
Magnitude	$$\mathbf z = x \mathbf 1 + y {\large\unicode{x1d7d9}}$$	$$y^2 = 1$$
Point	$$\mathbf p = p_x \mathbf e_1 + p_y \mathbf e_2 + p_z \mathbf e_3 + p_w \mathbf e_4$$	$$p_w^2 = 1$$
Line	$$\boldsymbol l = l_{vx} \mathbf e_{41} + l_{vy} \mathbf e_{42} + l_{vz} \mathbf e_{43} + l_{mx} \mathbf e_{23} + l_{my} \mathbf e_{31} + l_{mz} \mathbf e_{12}$$	$$l_{vx}^2 + l_{vy}^2 + l_{vz}^2 = 1$$
Plane	$$\mathbf g = g_x \mathbf e_{423} + g_y \mathbf e_{431} + g_z \mathbf e_{412} + g_w \mathbf e_{321}$$	$$g_x^2 + g_y^2 + g_z^2 = 1$$
Motor	$$\mathbf Q = Q_{vx} \mathbf e_{41} + Q_{vy} \mathbf e_{42} + Q_{vz} \mathbf e_{43} + Q_{vw} {\large\unicode{x1d7d9}} + Q_{mx} \mathbf e_{23} + Q_{my} \mathbf e_{31} + Q_{mz} \mathbf e_{12} + Q_{mw} \mathbf 1$$	$$Q_{vx}^2 + Q_{vy}^2 + Q_{vz}^2 + Q_{vw}^2 = 1$$
Flector	$$\mathbf F = F_{px} \mathbf e_1 + F_{py} \mathbf e_2 + F_{pz} \mathbf e_3 + F_{pw} \mathbf e_4 + F_{gx} \mathbf e_{423} + F_{gy} \mathbf e_{431} + F_{gz} \mathbf e_{412} + F_{gw} \mathbf e_{321}$$	$$F_{pw}^2 + F_{gx}^2 + F_{gy}^2 + F_{gz}^2 = 1$$

In the Book

• Unitization is discussed in Section 2.10.2.

See Also

• Geometric norm