Simple question concering rotation.

Anonymous · 2013-04-13T16:24:56

Hello fellows of gamedev.net. I've been struggling with a bit of a problem on my AI. Me and a friend are working on a space game. Our use-case is a basic kind of AI that will stop and turn to the player when the player comes near. The problem as follows: How do I find the (target) angular velocity that will rotate a ship towards a given point? The knee-jerk solution would be to create a look-at rotation matrix, but this isn't an option. The ship must be rotated indirectly by changing it's target velocity. I have looked in the book "Artificial Intelligence for Games, Second Edition", from page 180 and on, however this example use quaternions, not matrices like we do. I guess the basic idea would be to align the ships z-axis with the vector between the two ships, however I don't know how to achieve this( my math skills are lacking ) thanks in advance!

Math and Physics Programming

Started by Doublefris April 02, 2013 09:34 PM

12 comments, last by Paradigm Shifter 11 years ago

Doublefris

316

Author

April 12, 2013 03:01 PM

So I got it to work in XNA and it works beatifully, however using my own quaternion class or directx's quaternions the spaceship keeps 'flipping over' when you get behind on the Z axis it seems. Is there something specific I'm doing wrong?

my basic algorithm is :

Quaternion q1 = (shipforward, 0.0f)

Quaternion q2 = (shipposition - LookAtPosition, 0.0f)

then get the angular velocity using the method you described. weird thing is it works very well in XNA but trying to port it to my c++ engine keeps bringing this annoying bug.

A reason I thought of is that my division operator is wrong? what is the exact implementation of the division operator here?

alvaro

21,604

April 12, 2013 08:54 PM

I am not sure what (something, 0.0f) means. What is the 0.0f?

Doublefris

316

Author

April 13, 2013 04:06 PM

0.0f is simply the scalar( I guess real part) of the quaternion.

the f suffix means its a float.

Paradigm Shifter

5,832

April 13, 2013 04:24 PM

What problems with flipping are you having?

If you set up a quaternion with just a vector part and the w part being 0 you get a 180 degree rotation around the axis specified in the imaginary part... probably not what you want.

If flipping means you interpolate "the long way round" you can get rid of that by doing a dot product (in 4d) of the 2 quaternions and negating one if the dot product is negative.

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Simple question concering rotation.

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Simple question concering rotation.

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