vop How to Convert Quaternion to Angle?

[APG]

hello,How do I connect using vop?

thanks,please help me.

[catchyid]

Hi, I don't have much experience in VOP, so here is just a quick comment : a quaternion should be converted to an angle AND rotation axis (i.e. a quaternion to angle won't work, it must be an angle and rotation axis). Have you checked VEX functions, or VOPs? I am sure that conversion must be straightforward...

[APG]

1 hour ago, catchyid said:

Hi, I don't have much experience in VOP, so here is just a quick comment : a quaternion should be converted to an angle AND rotation axis (i.e. a quaternion to angle won't work, it must be an angle and rotation axis). Have you checked VEX functions, or VOPs? I am sure that conversion must be straightforward...

Thank you for your answer.

I get the angle just to rotate the model,How can I use the resulting quaternion to rotate my model?

[shawn_kearney]

Convert quaternion to matrix3 and multiply by position, with position on the top input such that the output is vector. Similar to "make transform".

I don't totally understand matrix as well as I'd like to, but essentially matrix3 can be used for rotation, while matrix4 can be used for both rotation and position/scale. They are applied by multiplying the position vector by the matrix.

For a 2D primer on the subject:

https://www.khanacademy.org/math/algebra-home/alg-matrices/alg-matrices-as-transformations/v/transforming-position-vector

For application in Houdini:

http://www.hossamfx.org/math-in-houdini/

Edited November 23, 2016 by shawn_kearney

[narbuckl]

Great resource on matrices and quaternions: http://www.tokeru.com/cgwiki/?title=HoudiniVex

[APG]

19 hours ago, shawn_kearney said:

Convert quaternion to matrix3 and multiply by position, with position on the top input such that the output is vector. Similar to "make transform".

I don't totally understand matrix as well as I'd like to, but essentially matrix3 can be used for rotation, while matrix4 can be used for both rotation and position/scale. They are applied by multiplying the position vector by the matrix.

For a 2D primer on the subject:

https://www.khanacademy.org/math/algebra-home/alg-matrices/alg-matrices-as-transformations/v/transforming-position-vector

For application in Houdini:

http://www.hossamfx.org/math-in-houdini/

Thanks for the answer.

I succeeded in calculating the angle,But the rotation center point of this angle is in world coordinates(0,0,0),It is not understand.

 

[shawn_kearney]

After posting I was a little worried about that. The math involved with actually getting a set of rads out of q doesn't look too crazy, if a little tedious (VOPs would be a tangle mess, better done in VEX).

http://stackoverflow.com/questions/12891843/java-converting-a-quaternion-into-radians-or-degrees

From here you could just take that, convert to deg and use "make transformation" binding your pivot attribute to the pivot parameter. I will poke around and see after the holiday here.

What exactly are you trying to do here? It looks like you're working with DOP geometry?

Edited November 24, 2016 by shawn_kearney

[shawn_kearney]

@APG Is this what you're looking for?

 

 

quat2.hiplc

Edited November 25, 2016 by shawn_kearney
optimized file

[APG]

1 hour ago, shawn_kearney said:

@APG Is this what you're looking for?

 

 

quat2.hiplc

thanks  for your answer.

see attachment,please.

 

rot_v004_apg.hipnc