First, the method has a name which sounds like it is returning some generalized scale value (albeit separately for each axis), but it is returning specifically the length of the 3 transformed basis vectors. That value might be interesting for some cases, but it should be named to indicate that operation rather than generically as GetScale(). Computing some kind of overall scale of 2D coordinates requires more complex calculations such as are (soon) being done in GetMaxScale2D() or GetMinScale2D().

The method is only used in one location in the impeller dispatcher:

It's not clear what is the best value to use in that case, but the length of the Y basis vector doesn't seem right.