Questions about calculations involving bones

rames44

Just starting with Daz scripting, so expect a whole sequence of newbie questions from me.

I'm trying to do some calculations involving bone positions.  I've read the documentation on DzBone and its base classes, and I do understand the difference between "local space" and "world space" when it comes to positions, rotations, etc.

Questions (all in the context of DzBone, even though many of the methods are in DzNode):

1. I assume that the "location" of a bone refers to its root (for lack of a better term).  Given the location and rotation or transform for the bone, how does one calculate the position of the bone's tip?  I see the DzNode.getEndpoint() method, but uncertain what space that is in and how it relates to getLocalPos()./ getWSPos()
2. How does the return value of DzNode.getOrientation() differ from the return value of DzNode getLocalRot()?  
3. For items that take a Boolean defaultVal=false  argument, if one passes in "true" for that, does this give you the value as if the bone's "positioning controls" were all set to zero?  (i.e. as if the bone in the figure is in the default pose's position)?

Thanks in advance!

Praxis

rames44 said:

Just starting with Daz scripting, so expect a whole sequence of newbie questions from me.

You will find mcasual's scripts to be an invaluable source of DAZ script examples: https://sites.google.com/site/mcasualsdazscripts9/home

rames44 said:

1. I see the DzNode.getEndpoint() method, but uncertain what space that is in and how it relates to getLocalPos()./ getWSPos()

I think it's in LocalSpace - see e.g. mcasual's usage in https://sites.google.com/site/mcasualsdazscripts7/mcjchainchainchain

As for your questions 2 & 3: I don't know - I'd like clarification too.

 

rames44

Thanks - I’m well aware of mcasual’s awesome body of work. It was what inspired me to dip my toe into this, and I am gradually deciphering how some of his scripts work.

i just wish the Daz docs were a bit more detailed.

mCasual

when you zero-pose a figure ( maybe also zero-morphs ) the figure is in a T-Pose, which is the way the figure was rigged 

the bone.getEndPoint() function gives you the position of the end-Point in World space

but as we'll see below this doest mean it's the position where we expect the hand joint to be

to get the world-space endpoint, you'd probably be better using the world-space joint position and the children-bone joint position

example for Genesis3 zero-posed but not zero-shaped

skeleton = Scene.findNode( "Genesis3Female" );
foreArm = skeleton.findBone( "lForearmBend" );
hand = skeleton.findBone( "lHand" );
pHand = hand.getWSPos();
pForeArm = foreArm.getWSPos();
foreArmEndPoint = foreArm.getEndPoint()
debug( "pHand = " + pHand )
debug( "foreArmEndPoint = " + foreArmEndPoint )
foreArmVector = pHand.subtract( pForeArm );
debug( "foreArmVector " + foreArmVector );

Executing Script...
pHand = [63.6351,146.046,2.78125]
foreArmEndPoint = [50.3839,145.886,-0.804868]
foreArmVector [26.5685,-0.98024,6.63302]
-------

my genesis3 was zero posed

here you can see that the position of the hand and the position of the endPoint of the foreArm don't match

so the world-space  positions of the hand and foreArm are better if you want real positions

-----------

i think the endpoint parameter is more a convenience for rigging, by that i mean it's used when comes time to  bend the skin of an elbow for example

------------

since the finger tips dont have a child bone, you could parent and position null nodes at the finger tips

and get your null node using

lIndex4 = lIndex3.getNodeChild( 0 );

 

===========================================

getOrientation() tells you how the 3 hinges that make a joint are oriented

so here too its mainly a rigging convenience, well actually historically i found this brain-stretching to work with,

but i did fight the good fight when i made a script to rig mirrors on my VW Transporter

https://sites.google.com/site/mcasualsdazscripts3/mcjchangeorientation

getLocalRot() gives you a Quaternion, that describes how that bone was twisted and bent from its initial zero-pose , to be in its current orientation

Local means, imagine the figure was in  the zero-pose ( t-pose )  and now the foreArm is bent 90 degrees

getLocalRot() would give you a quaternion that rotates something 90 degrees around the Y Axis

skeleton = Scene.findNode( "Genesis3Female" );

foreArm = skeleton.findBone( "lForearmBend" );

debug( foreArm.getLocalRot() )

the result : [-0.00681274,0.707073,-0.00100848,0.707107]

quaternions, if you dont know are not euler rotations like we see in the parameters tab : rotx roty rotz

instead they are of the form x, y, z, w

where xyz are like a hinge arouns which the rotation will occur and w indirectly tells the angle of the spin around that hinge

so you have to use functions that accept quaternions to manipulate them

say you have 2 vectors you can get the quaternion for the angle between those 2 vectors

by doing rotab = veca.getRotationTo( vecb );

then you can do rotForeArm = foreArm.getWSRot()

then rotForeArm = rotForeArm.multiply( rotab )

foreArm.setWSRot( rotForeArm );

and we rotated the foreArm by the angle between veca and vecb

i do most my rotation tricks using the getWSpos, getRotationTo, multiply, setWSRot functions

you just have to figure if you need to do veca.getRotationTo( vecb ) or vecb.getRotationTo( veca )

the other functions i use a lot for the 3D space gymnastics are  thisStick.getWSRot().getYAxis() 

which gives you the YUp vector for theStick

 

 

 

Praxis

mCasual said:

...(a whole lot of useful stuff) ...

Thank you maestro!