Dual Quaternions

Hello,

I've been reading through Game Engine Architecture, and must commend you on an excellent book. I'm a lead-programmer with just over 10 years experience making games, so I'm not directly in the target audience, but I've still found it a very interesting read. I just wish it had existed a few years earlier!

Anyway, the section on Dual Quaternions was something that interested me - I hadn't heard of them before, and the possibility of representing rotation, translation and scale in 8 floating point numbers sounded useful - to good to be true really! However, having skimmed through the cited .pdf file, I can find no mention of them representing scale, and this resource http://isg.cs.tcd.ie/kavanl/papers/sdq-tog08.pdf suggests also that they cannot represent scale. Quote:

"Dual quaternions cannot represent non-rigid transformations, such as scale and shear. This means that dual quaternion skinning, unlike linear blend skinning, is restricted only to rotating and/or translating joints."

Anyway, thought I'd mention it. If I've misunderstood them and scale is possible, then apologies. If not, then perhaps a section for corrections on the website would be useful.

Kind Regards,

Andy Weinkove.


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Hi Andy,


You are quite right, that is an error.  Dual quats represent a combined rotation and translation... basically a "screw motion" and are incapable of describing any kind of scaling transform.


Cheers,
J