View Axis Orientation
Axis Orientation refers to the direction that an axis of a given object is favoring. As discussed in the topic “Axis”, there are several different coordinate spaces that are at play at any given time in a 3D scene or project. Ultimately, they must all play well together, and it helps if you understand what’s going on. It can be confusing, but just take it in a bit at a time, and soon you will have a good feel for how it all works.
Typically, axis orientation is something to be aware of when you are working with hierarchies of objects, and you want the objects in that tree to work together as a cohesive group. This is especially true when you are building skeletons of joints for character animation. (Note: “character animation” can refer to organic creatures as well as mechanical objects that require a skeleton to perform the way you intend, whether or not a similar thing in the real world would have a skeleton.) Joints have a preferred direction, and they point along their Z axis. Should joints get created that do not point along their Z axis, you will need to re-orient them to correct that. In addition, it is possible for joints to point properly along their Z axis, but be misaligned with the other axes, as defined by their parents. For chains of joints to behave properly, all of the joints in the chain need to have the same orientation. In other words, if front is Z, then top is Y, and all of the joints in the joint chain need to honor that axis alignment.
Quite often, you will create scene elements that differ from the world orientation of Y up, Z front. If possible, you will have a much easier and more predictable experience if you orient your objects similarly to the world (unless you have specific reasons not to).
In all, stacking up objects in a hierarchy can really play with your head when it comes to controlling rotation values, due to the complexities of the math involved (see, math is important—you should have paid more attention in class!). There are many resources online which discuss the topic of rotations and their behavior, but the best discussion comes from Cactus Dan, a favorite among Cinema 4D users. Look up his character tutorials. There’s real gold there…