Is there a way to revert a volume's transform back to normal?

[magneto]

Hi,

I am trying to revert the rotation of a volume so it aligns with the world. I tried setting the primitive intrinsic, but if you set it to identity, then you lose the scale. Since it's absolute, I am not able to apply the inverse of this transform either.

Should I use the explodematrix expression?

I am actually trying to create a bounding box that has the same size and orientation. Setting the orientation of the box is easy but I am not sure how else I can find out the size of the volume since it can be scaled. But Volume Slice SOP is able to do this accurately it so there must be a way.

Any ideas?

Thanks

[sanostol]

do You have a example file, demonstrating what You try to achieve?

[magneto]

Thanks sanostol. I attached the file. Basically trying to create the same bounding box of the volume you see. But I don't want to use OBB algorithms because the transform of the volume is known.

I actually came up with a solution yesterday by sampling the positions of the corner voxels, which when you account for the voxel size, seems to work. Just didn't think it would be this complicated

vol.hip

[petz]

is this what you are after?

petz

vol_1.hip

[magneto]

Thanks petz, very clever trick. Your solutions are always the most elegant

EDIT: Do you know if I can use the same idea to extract rotation? Because if I extract it using the same function, then I am not sure how to apply it to an identity matrix. There is only a rotate function that rotates a matrix around an axis.

How can I use this extracted rotation to orient another geometry?

EDIT 2: In other words, I want to reset the translate and scale of the matrix so I am only left with a rotation matrix. I tried extracting and rotating by x, y and z separately, and also converting the matrix (after from matrix4 to matrix3) into a quaternion, and then applying but it seems inaccurate.

Do I have to use something like the QR decomposition?

Any math experts?

Thanks

Edited November 30, 2013 by magneto

[anim]

one way to create rotation matrix rotm from transform matrix mat

vector euler = cracktransform(0, 0, 1, {0, 0, 0}, mat);
matrix3 rotm = qconvert(quaternion(euler,0));[/CODE]

[magneto]

Thanks anim, do you think that's accurate enough? I tried it for some stuff but it seems off when compared to the full matrix itself, which of course also have a scale I am trying to get rid of.

[Guest mantragora]

Why do I feel like I'm watching Maya thread ?

[magneto]

Why do you say that? Were matrix operations common in Maya? It has been a long time since I wrote tools for Maya, and for a good reason

[Guest mantragora]

Yeah, I hate Maya. I tried get into it couple times last 5 years. Once I have to script every little shit in it or use this f*cking linking editor I'm out. It's the end of 2013 and in Maya it's still 90's.

[anim]

Thanks anim, do you think that's accurate enough? I tried it for some stuff but it seems off when compared to the full matrix itself, which of course also have a scale I am trying to get rid of.

do you have example of that?

[magneto]

Thanks anim, I will make a scene file today