My first post here and I hope it isn’t too basic or stupid. I’ve started making a model of a human in Blender to be posed in a scene also to be composed in Blender, and it occurred to me that the center of the model (the 0,0,0 point) might be important. In other formats, like VRML it can be important, especially when inserting an object into another scene. Is there any reason why it might be important in Blender? For example, seeing what an avatar sees is most easily done if the camera can be put at any avatar’s 0,0,0 point, where its eyes are, so that no offset is needed.
Another related concern, which I’m not quite sure how to express properly, is the base of an avatar’s skeleton. In VRML (I have most experience there) the base is at the pelvis. This is something I always thought was a bad idea for a few reasons:
we naturally think of ourselves as being where our eyes are so that should be the center
a diagram of a kinematic skeleton in the standard VRML humanoid starts with the pelvis at the top of the chain, which is difficult to understand and looks quite counterintuitive. If the kinematic chain starts at the head then diagrams are clearer. (Probably not a concern in Blender.)
during movement a real creature or person attempts to minimise movement of the head, or at least smooth it out so that in a sense all body movement relates to the head. That is, shouldn’t a kinematic chain start from the head? If so would this mean a nod of the head would end up moving the body instead of the head? Or is there an easy way around that?
almost every avatar will have eyes, but many don’t have a pelvis. For example where is the pelvis in a centipede, an octopus, a centaur? Again, this might not be important in Blender, which seems more pragmatic and solution oriented than VRML, which tends to be more rule-based.Is there anything I should be aware of about centering my avatar in Blender before I go too far and end up making a big mistake?
Also, I’ve started building my model and heard recently that it could save a lot of trouble later to make the armature first. Is this right? Anybody here do it that way?
I haven’t any experience moving Blender models to other formats, so I’ll just mention some animation considerations. In free fall, the body has a center of gravity about which it rotates. When animating motion, jumping, running, falling, climbing, it’s much easier if the armature begins at that point, rather than somewhere else. In humans, the center of gravity is somewhere near the pelvis (depends on physical conditioning, weight, gender, etc, but the pelvis is pretty close for most people.) In creatures that don’t have a pelvis, they still have a center of gravity.
There are other benefits. Motion of the extremities begins at the center, and works out to the edges. An armature that took an IK chain from the hand all the way to the toe would be very difficult to work with. Possible, by “pinning” bones to certain locations temporarilly, but a real pain to work with. It’s much simpler to move hands and feet and the head from the center, and move the center when appropriate.
Thanks Orinoco. I’m building this solely for use inside Blender, having become tired of VRML. After having used VRML for a little over a decade I’d become more and more disillusioned at how little progress it made over that time. I have some experience with Lightwave3D and have been using POV-Ray since the beginning when it was called DKBTrace. I sorely wish I’d begun using Blender years ago. It is brilliant and I have a lot of catching up to do. It’s never too late I guess.
I hadn’t thought of center of gravity. Somehow I’d thought Blender worked that out itself. That would be an excellent reason to center on the pelvis, between the hip joints. When a gymnast straightens their body at right angles across a horizontal bar, with arms by their sides, and the bar at their hip joints, then balance is achieved.
Starting the IK chain from the center does make good sense. I can see how reversing the order could get annoying.
Well, I recall taking a look at POV-Ray when it was first released as POV-Ray, and thinking I didn’t want to draw by mathematically specifying everything that showed up, and dropped it like a hot rock. Oh well.
As to catching up, good luck. The developers seem to be adding features faster than I can keep up with them, at any rate. Once they finish the refactoring and anyone with a working knowledge of Python can write plugins, watch out. This software is going to explode.
Anyway, great avatar you’ve got there, anyone flashing a triquetra is ok in my book. If you have any more questions, don’t hesitate to ask, everyone is very friendly and helpful here, except for the few that ain’t, and watch out for drag0ns. Welcome to BlenderArtists.
