# How are quaternions specified?

**URL:** https://tech-community.robotics.abb.com/t/how-are-quaternions-specified/11805
**Category:** RobotStudio
**Tags:** signal-analyser, quaternions
**Created:** [February 25, 2025, 1:48pm UTC](https://tech-community.robotics.abb.com/t/how-are-quaternions-specified/11805 "2025-02-25T13:48:43Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![nihm20](https://avatars.discourse-cdn.com/v4/letter/n/3be4f8/32.png) [@nihm20](https://tech-community.robotics.abb.com/u/nihm20)
#### Post date: [February 25, 2025, 1:48pm UTC](https://tech-community.robotics.abb.com/t/how-are-quaternions-specified/11805/1 "2025-02-25T13:48:43Z")

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As I understand it quaternions can either be specified with the scalar part first or last as according to

q = w + xi + yj + zk  
or  
q = xi +yj +zk + w

where w is the scalar part. I was setting up my signals for my signal analyzer so I was wondering in which order RobotStudio defines quaternions for orienation, does Q1 or Q4 represent the scalar part w?

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<div class="post-metadata">

### Author: ![nihm20](https://avatars.discourse-cdn.com/v4/letter/n/3be4f8/32.png) [@nihm20](https://tech-community.robotics.abb.com/u/nihm20)
#### Post date: [February 25, 2025, 1:50pm UTC](https://tech-community.robotics.abb.com/t/how-are-quaternions-specified/11805/2 "2025-02-25T13:50:00Z")

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![](https://europe1.discourse-cdn.com/flex005/uploads/robotics1/original/2X/e/e3534df70c2a202bc55ba482763dced9828f663d.png)

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### Author: ![Kenny-RenYi\_Jiang](https://avatars.discourse-cdn.com/v4/letter/k/e480ec/32.png) [@Kenny-RenYi\_Jiang](https://tech-community.robotics.abb.com/u/Kenny-RenYi_Jiang)
#### Post date: [February 26, 2025, 1:21am UTC](https://tech-community.robotics.abb.com/t/how-are-quaternions-specified/11805/3 "2025-02-26T01:21:41Z")

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I believe it’s q = w + xi + yj + zk. (1,0,0,0) corresponds to no rotation.