How can I convert a Quaternion to a direction vector?

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how i can Converting a Quaternion to a Direction Vector? i have two Quaternion and i need to convert the two Quaternion to vector3

and used the vectors in Quaternion.LookRotation(v3,v3)

Quaternion targetRot = Quaternion.LookRotation(myForward, hit.normal);

Quaternion targetRotation = Quaternion.LookRotation(targetDirection,hit.normal);

http://www.2shared.com/document/2djAJSdi/save.html

and

convert : Quaternion targetRot to vector3 targetRot
convert : Quaternion targetRotation to vector3 targetRotation

and used the new vector in: Quaternion AllTarget = Quaternion.LookRotation(vector3 targetRot, vector3 targetRotation);

Answer 1

Best Answer

Answer by Bunny83 · Aug 28, 2013 at 10:51 PM

A quaternion doesn't have a direction by itself. It is a rotation. It can be used to rotate any vector by the rotation it represents. Just multiply a Vector3 by the quaternion.

     Vector3 targetForward = targetRot * Vector3.forward;
     Vector3 targetUp = targetRot * Vector3.up;

What axis you need you have to figure out yourself since your code is just an abstract collection of code fragments.

Just to be absolutely clear for beginners: When you say "Which way is this Quaternion's up?" or "Which way does this Quaternion point forward?" what you probably actually mean is:

"If you take something which is standing straight up and forward, and apply the Quaternion to it, which way is the forward vector now?"

The example code above provides exactly that information.

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TheMasonX · Dec 11, 2015 at 10:14 AM 0

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Thanks for the answer! $$anonymous$$ore importantly, thanks for the explanation/clarification of the underlying question in the second half; it really explains WHY this gives the intended result, rather than it being just another abstract operation that spits out the intended result.

AndyMartin458 · Nov 17, 2017 at 02:06 PM 0

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Sorry, I had it backwards, thank you for the explanation.

Bunny83 AndyMartin458 · Nov 17, 2017 at 04:08 PM 0

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Uhm, what do you mean? Your code example doesn't work. You have to do

 Quaternion * Vector

That's what The_$$anonymous$$ean_Fiddler said and that's what is written in my answer.

Quaternions basically work like a matrix multiplication which is also right to left. The $$anonymous$$VP matrix need to be multiplied in reverse order P * V * $$anonymous$$

Answer 2

Answer by The_Mean_Fiddler · Jun 26, 2015 at 09:04 PM

You have to do Quaternion * Vector3

Vector3 * Quaternion gives an error

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Mr-Mechanical · Aug 09, 2015 at 05:43 AM 0

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Wow. Thank you. This fixed my error!

Siloaman · Dec 15, 2015 at 10:22 PM 1

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THAN$$anonymous$$ YOU!!!

THIS ONE DETAIL GAVE $$anonymous$$E 5 HOURS OF GRIEF!!!

THAN$$anonymous$$ YOU!!!

Quasimodem · Jan 20, 2016 at 11:39 PM 0

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This caught me too. $$anonymous$$ultiplication is commutative, dammit!

It'd sure be nice if Unity would add

public static Vector3 operator *(Vector3 point, Quaternion rotation);

to the Quaternion class as well. Normally, you could do this yourself as an extension method, but unfortunately, C# doesn't allow you do make extension methods from operators. Bummer.

Eno-Khaon Quasimodem · Jan 21, 2016 at 04:42 AM 2

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$$anonymous$$ultiplication is commutative

True. $$anonymous$$ultiplication IS commutative.

Quaternion multiplication, however, is not commutative. When you multiply with a quaternion, the process can only behave in one manner.

See https://en.wikipedia.org/wiki/Commutative_property for details.

Bunny83 Quasimodem · Jan 21, 2016 at 06:00 AM 1

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Some additional information on the noncommutativity of quaternion multiplication. And just in time there's now a Numberphile video on quaternions ( extra bits ) which might help to get a better understanding of how they work.

Answer 3

Answer by edthered1009 · Feb 18, 2019 at 11:05 PM

Extremely simple. Quaternion.eulerAngles makes it a Vector3. :)

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Bunny83 · Feb 18, 2019 at 11:23 PM 2

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This makes no sense. Yes, eulerAngles is represented as a Vector3 because it represents 3 angles, but this does not represent a direction vector.

edthered1009 Bunny83 · Feb 20, 2019 at 10:20 PM -1

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When did he ask for a direction vector? He asked for a Vector3.

[I] have two Quaternion[s,] and [I] need to convert the two Quaternion[s] to vector3[s.]

. Pay attention. Edit: Just realised he did mention direction vectors, but I think he is just using the wrong terms. Thanks for trying to help, though!

How can I convert a Quaternion to a direction vector?

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