Transform.rotatepivottranslate

[rob-bateman]

I've seen the attr transform.rotatePivotTranslate around quite a bit. Does anyone want to have a go at explaining how it is calculated? Try the following.

create a poly cube.
move the rotate pivot.
run "getAttr pCube1.rotatePivotTranslate"
rotate the cube.
run "getAttr pCube1.rotatePivotTranslate"
now move the pivot again.
run "getAttr pCube1.rotatePivotTranslate"

The API and node docs are a bit thin on the ground with descriptions on this attribute, and more importantly how that value is calculated. Has anyone dealt with this value before, and know how the value is calculated?

[vhof]

That's weird, but I've noticed, that it's enough to move the pivot once to achieve different from 0,0,0 value.

How -
1) rotate the cube not around but in the direction of the axis which you plan to move the pivot
2) move the pivot
3) check the values.

[talama]

I'm beginning to study the maya api (OT a big tanks to robert for his great site, i've been looking there quite a bit in the last few weeks /OT) so take this with a grain of salt. As an exercise i tried to build my own point constraint and what i found is that the rot. pivot trans. is there to compensate for the fact that, if your object is rotated and you move the rotate pivot point, its position should change.

About how it is calculated, i'm not that strong at linear algebra but it seems to me that it's very "similar" to how the value in a rotation matrix are computed from the rotation angle.

Ex. Let' say you have a cube at the origin that is rotated 30 deg on the x axis and then you move the pivot poin 10 unit on the Z axis.

You have ;
tr = pivot point translation = 0 0 10
cos (rotX) = 0.866
sin(rotX) = 0.5

And
Rotate Pivot
RPx = 0
RPy = 5 = tr * sin(rotX)
RPz = 8.66 = tr * cos(rotX)

Rotate pivot translate
RPTx = 0
RPTy = -5 = -(tr * sin(rotX)) = -RPy
RPTz = 1.34 = tr - (tr * cos(RotX)) = tr - RPz

With RP + RPT = 0 0 10 = pivot point translation

I wasn't able to figure out the general rule behind this, but it seems to "make sense".
What is cool is that using this two value you can for example get the full amount of translation an object represent in world space, no matter if freeze transform has been applied or the pivot moved ecc. ecc.

hope it helps (and really sorry for my english, working on that too)

Ciao

Luca