#R4 IK
21 messages in this thread
Jonas,
While it's on my mind, there are a couple of typos I found so far in the
manual. Page 87, #4, has you clicking on the wrong thigh. A warning might be
in order for people to leave out the curtains in the Randy the Egret animation,
or that could make for a reeeeally long coffee break. <g> Next, anybody who's
trying to follow the settings on page 98 could get really confused. Quite a
few of them are reversed. This could make for a really strange contortionist.
<g> And I thought my son was the only one who could chew on his toenails.
Yuck!
I know you guys have been working with this for quite a while already, but a
few of us have never done this before. A few more examples to work through
would be of great help. This is all kind of confusing at first.
I picked up Viewpoint's skeleton. Maybe you or someone else has some idea what
joint parameters might be for each vertebrae, and would they vary along the
length of the spine? Knees and ankles are pretty easy, but it's hard to look
at your spine. <g> Also, I started with the tailbone as the parent. Has
anybody got a guess what vertebrae the ribcage might link to? At present I'm
still having a real hard time with paths. That could very well be brain fade
on my part, though.
Roger D.
What do you mean by joint parameters for each vertebrae? In terms of what rib
attaches to what vertebrae, that is a tricky question, if you really do not
care to much about anatomical accuracy, then the rule of thumb is: starting
with the first thoracic vertebrae attach the first rib, then attach rib 2 to T2
down to T12 which is the last thorace thoracic vertebrae. Now for some more
detail, the first rib articulates below the clavicle without directly attaching
to the sternum, ribs T2- T7 attach dirctattach dirctly to the sternum with T8,
T9, andT10 attach to the sternum via a costal cartalidge. T11 and T12 are not
attached to the sternum and are thus called floating ribs. A very good
reference for this is Grant's Anatomy. As a general answer regarding the
vertebrae each vertebrae is able to flex, extend, rotate, and lateral sidebend.
The first cervical vertebrae can translate on the occipital condyles. A good
reference for this is a series of books on functional anatomy by Kapanji. Hope
this helps Sam Coor
>> The first cervical vertebrae can translate on the occipital condyles. <<
Huh????!!!
The occipital condyles are on the bottom portion of the skull on the occipital
bone. If you look at the base of the skull there is a large hole called the
foramen magnum, on each side of the f. magnum are two covex shaped bone
formations. Those are the condyles and articulate with the first cervical
vertebrae. The anatomy of that particular "joint" allows for some sliding or
transalatory motion. Sam
Did you learn all this to model the skull or are you involved in the medical
profession? Curious.
I am a neurologist that is involved in producing interactive medical titles
and currently finishing up the final stages of an anatomically accurate mesh of
the whole skeleton. Most of it is completed but we are trying to reduce the
overall vertice count without comprimising its accuracy. Sam
Guess that explains it. Thanks for the help so far.
Roger D.
Welcome to the world of 3D animation. Good luck in you endeavors.
Thanks, I have been using the forum mainly as a browser since version 1 and
have received alot of help and hints! Great source of information and
resources. Sam
>> The first cervical vertebrae can translate on the occipital condyles. <<
> Huh????!!! <
Oh, you know: "Da neck bone's connected to da head bone!" <G>
Ah, now it makes sense. <g>
For IK vertebrae try the following –
Think how far the _entire_ back bone can bend in _either_ direction. Dive that
angle by the total # of vertabrea and apply the resulting fraction to each.
Combined, they will then bend accordingly.
– Phil
Sam,
What I mean by joint parameters is in IK (Inverse Kinematics) in R4, you can
define joint parameters, i.e. what percentage they can be rotated on X, Y, and
Z axes. I was just wondering what level of mobility each vertebrae would have
in comparison to the ones next to it. Say, so many degrees forward, and so
many degrees side to side, and so many degrees back. I suppose someone could
just guess, but what the heck, if you can just punch in the right number, why
not? Thanks for the help on the ribs.
Roger D.
In terms of the exact degrees that is a very difficult question to answer, and
again it would depend on the level of accuracy you are looking for. There are
a number of very good references regarding joint motion if you are looking for
accuracy, if you are not looking for accuracy than as a general rule of thumb
each region of the spine acts about the same. Break up your vertebral column
into 3 sections, cervical, thoracic, and lumbar. Assign each section there
natural curve where the cervical spine has a lordosis, the thoracic spine has a
kyphosis and the lumbar spine has a lordosis. After you have set up those
curves than looking at each individual vertebrae per section rotation can be
set that the vertebrae does not override the articular facet joint. In terms
of flexion and extension, with flexion you will have to make sure that you can
flex only to the degree that you do not put the anterior portion of the
vertebral body into the other and you will have to compress the disc in
proportion to the amount flexed. In extension make sure that the spinous
process's don't run into one another. If you want to be absolutely precise,
very, very tough I will again refer you to the 3 volumn set on biomechanics by
Kapnji, if you want something more concise, if you have access to a medical
library do a medline search focusing on the journal SPINE with the keywords
vertebrae, and range of motion. That should get you started. Sam
Hello Sam,
How are ya? I must say that your "from-experience" explanations concerning
medically-realted issues is certainly interesting. Nice stuff.
One thing though, after watching certain folks (say, like gymnasts) on TV and
then consulting my own set of vertebrae, I have to mention that the exact
amount of flex between them can change vastly from person to person!<huge grin>
So, to RogerD: Make sure you consider the age and life-style of your skeleton
before locking in those joint constraints!<g>
-Alan (just want my back to flex a _little_ more…)
Alan ,things are going well thanks. The amount that the vertebrae is limited
in motion is not necessarily age related in terms of the vertebrae themselves.
Most of the time, barring severe arthritis, trauma, etc., the range of motion
of the spine is limited by the surrounding soft tissues. As an example- stand
erect with your feet together then flex at your waist keeping your knees locked
in extension and touch your toes. The main limiting factor in the ability to
touch your toes are tight hamstrings! not a tight vertebral column. So if you
are modeling an animation of vertebral motion in the so called "vacuum" the
motion of each vertebrae is essentially the same across all age levels until
you start addressing degenerative changes. Sam
Sam,
One never knows what one is going to learn on the forum. <g> I've found this
thread on human spinal motion most interesting. I think you're knowledge about
human anatomy and motion is very valuable to the forum. Especially with all the
interest in character animation.
Just wanted to say thanks,
John
Sure, anytime its the least I can do since I have certainly learned alot from
everyone on this forum. Sam
Sam,
Could you reccomend any good texts on the subject of range of motion and
biomechanics?
Thanks,
Andy
There is a 3 volumn set by Kapanji, I don't remember the name specifically but
they are broken down into vertebral motion, and axial motion. They are soft
covered and not that expensive, just call up any medical book store and asked
for Kapanji's text. They are pretty much the gold standard. Just a word of
caution, the way they are printed it looks like pretty simple reading, lots of
line illustrations but you will need to get a good working knowledge of the
anatomy terminology and the way they break the different 3 dimensional planes
down which is different than animation planes. They assume you have a good
knowledge of this already, if not pick up a good medical dictionary such as
Dorland's. Hope this helps Sam
I think *I've* started addressing degenerative changes, Sam.<g>
Thanks again for the good info,
-Alan