Author Topic: What is the defination of orientation.x, orientation.y...  (Read 32 times)

Qriver

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What is the defination of orientation.x, orientation.y...
« on: September 11, 2018, 04:38:51 AM »
Dear all,
I have checked the paper of Peter Mahler Larsen, but I did not see the defination of orientation.x, orientation.y, orientation.z and orientation.w calculated by PTM, can you tell me the difference of these four parameters?
Thank you!
Shuai

Alexander Stukowski

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Re: What is the defination of orientation.x, orientation.y...
« Reply #1 on: September 11, 2018, 09:44:44 AM »
Shuai,

They are the 4 components of the quaternion used to express the local lattice orientation computed by the PTM modifier for each identified crystal atom. Please see the Wikipedia if you are not familiar with quaternions and how they can be used to express orientations: https://en.wikipedia.org/wiki/Quaternions_and_spatial_rotation

The PTM paper mentions a "right-handed orthogonal matrix Q" being computed for each atom, which is basically a 3x3 rotation matrix. In OVITO, this orientation information is translated into the more compact quaternion representation and stored in the "Orientation" output particle property.

-Alex