In the FaceNet paper, under section 3.2, the authors mention that:
The embedding is represented by $f(x) \in \mathbb{R}^{d}$. It embeds an image $x$ into a $d$-dimensional Euclidean space. Additionally, we constrain this embedding to live on the $d$ dimensional hypersphere, i.e. $\|f(x)\|_{2}=1$.
I don't quite understand how the above equation holds. As far as I understand, the $L_2$ norm is the same as the Euclidean distance, but I don't quite understand how this imposes $\|f(x)\|_{2}=1$ criteria.