Genesis 3 - why are some joints not aligned?
Singular3D
Posts: 606
I really try to understand the rigging in Daz Studio. While examining Genesis 3 in detail, I got stuck on two issues.
1) Why are child bones not connected to their parent (see knee of Genesis 3 female)?
The Thigh Twist ends at the knee, whereas the Shin just starts below the knee. This may make sense in order to get the pivot for the shin to the right place and keep the orientation of the Thigh Twist as it is.
2) Why is the Shin Bone not aligned to the end point? In most tutorials I found, the bone was aligned to the end point in the end. Here the bone end/orientation is different from the end point of the bone. Is there a reason for that? Also the child bones are not connected, but off with white dotted lines.
In general I ask myself, why the bone is not always defined by the start and end point. There is also a rotation defined. This will give the bone a direction, but in order to define the length of the bone a length value should be sufficient. So what is the end point needed for?
Thanks a lot in advance for any helpful information and deeper technical documentation (e.g. links).
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Comments
Have they really made bones for the knee caps?
https://en.wikipedia.org/wiki/Sesamoid_bone
No, sorry for the misunderstanding. No bone for the knee cap. There is just a gap between the thigh and the shin bone.
Well, it may make sense, that there is a gap, but I really wonder about the second thing (bone alignment and end point).
To answer your question, you have to understand how bones function:
The point that is at the beginning of the bone is called the "Center Point". It is the Center of motion. The "End Point" is at the end of the bone. The line drawn between them is the "bone" that you see. The bone will be rotated on the X, Y, Z axis from the Center Point.
Now, you will not always WANT the Center point to be at the End Point of the last bone, because the rotation will be weird. Look for example the thighs of the figures. It's impossible to create the right movement if they would not be moved.
The same thing applies to the Shin bone and the Ankles.
If the bone was starting at the End Point of the last bone, it would not bend correctly.
At the same time, setting the End Point of the previous bone to the Center Point of the Child bone..... this would rotate the bone and cause odd movement again.
Humans have much more bones, which have different shapes to allow us the movement we have. In 3D you only have the lines (at least in DAZ Studio) so you have to "cheat" by placing the bones in different places, even if it disjoints them.
Does this answer your question?
Thanks for the explanantion. It definitely makes sense. I understand the 'disjoint' fact. Nevertheless I'm still struggeling with the second issue
Look at the Shin bone end point...
There is a center and an end point of the Shin bone. I would expect that the bone is located between the center and the end point. As you can see in the second image, the end of the bone and the end point are not at the same place (not aligned). I made a circle around it. If the bone is defined by center and end point, why do I need an orientation? If I align the bone, end point and end of bone are at the same place again, but if I move the end point after that, the length of the bone is affected, but not the orientation.
- So, what is the reason behind the fact that Genesis 3 female Shin bone is obviously not aligned?
- Why do we need orientation values, when the bone is defined by center and end point anyway?
- Does the length of the bone have any influence on the weighting? Isn't the orientation the only thing that counts?
I can only make a guess here. The person performing the rigging probably used the Orientation sliders to adjust the bone. You see, the Center Point is the origin of motion. The End Point however is just used to help you position the bone. Orientation of the bone is calculated by the program when you tell the bone to "align" with the end point. You cna however use Orientation sliders to further adjust it. It's just sometimes easier to use this than to specify an End Point.
There might be a different reason though, but I have no clue what it could be at the moment.
Same as answer above - it's another tool to help you setup the bones. Sometimes its easier to specify and End Point and Align the bone, sometimes its easier to just change the orientation. It's like moving the Bend, Twist, Side-Side sliders when posing a figure.
It makes it easier sometimes.
To my knowledge - the length of the bone is not doing anything important. (I may be wrong here, however I have never experienced change in bone length to do anything when I rigged figures in DAZ Studio)
Well, to be completely honest - sometimes you will setup the rig so that the Child Bone will start its Center Point at the End Point of its Parent. So then you will make the bones go from Center to End point to make it look like a logical skeleton. But outside of that - not really.
Does this answer your questions?
Hi Thomas,
Thanks for your reply. I'm used to work with all kind of other software and try to understand the specifics of Daz Studio and Genesis 3.
When I rotate the bone, the end point is rotated like a satellite. So it seems that the bone orientation is critical for bending and twisting. The end point indirectly controls the length of the bone and thus scales the limb. It's not relevant though for the rotation.
I try to setup the Genesis 3 rig in another program (Cinema 4D) in order to be able to use the Daz assets there as well. So I'm glad about all information about the G3 rigging that I can get,
Walter
Well, I port models from other software into DAZ Studio so I guess you are doing the reverse of what I am doing. Then again I mostly import an OBJ file and then transform it into a figure in DAZ...
As far as i know the only use for the endpoint is when using "PointAt" for the bone. Since there is no such thing as a "main axis" or something like that for a bone, "PointAt" uses the line from origin to endpoint of a bone to point to the "PointAt" target.
Exactly. I like the DAZ models, but getting them to work natively in Cinema 4D will ease the use of other features of this software. I'm almost there... I could export the mesh and re-rig it, but thus I would loose the option to work with morph packages, as they are often driven by the rotation and weighting. The quaternion weighting works the same way in Cinema 4D, but the rotation is different. It can be adjusted, but I need to understand how.
The rotation axis (e.g. twist) is defined by the orientation of the bone and not by the end point. Just Twist the Shin and you'll see. Thanks for the hint about this "PointAt". I have to look at that and what it really does.
As noted above, the end point is used with the origin to define the direction of the point-at vector - that is usually along the bone, but doesn't have to be.
The things that matter for the bone are the origin, the orientation and the rotation order - those determine the point about which the bone rotates, and the alignment of the twist (first axis in the rotation order) and the two rotations. The length of the bone in the viewport is purely a visual feature, determined by the location of the origin and end point (even if the bone's orinetation means the end point is off the bone); it has no functional significance.
Hi Richard,
Thanks a lot for joining in. I think I understand now how it works.So the end point is not relevant for the bone rotation.
I think I have to do some tests next to see if there are any open issues.
All the best
Walter
I'm also confused by this characteristic of DAZ Studio which is different from any 3D applycations I'm familiar with. I'm still trying to figure out how does the start&end point plus orientation&scale settings makes any sense. If the end point is not relevant for the rotation why does it exists?
BTW why do DAZ have to make it self so difficult to be understood in so many ways....