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# rotation <=> dircos

Phenom

Hello,

Could someone indicate the exact operations FEMAP does when transforming 3 rotations to a dircos matrix? I can't replicate exactly the calculation...

Thanks!

AP

3 REPLIES

# Re: rotation <=> dircos

Phenom

Do you mean an API for converting a sequence of rotations about the fixed axes X, then Y then Z into direction cosines with respect to the same axes?

The attached link may be useful, if perhaps much more than you need...

http://www.mech.utah.edu/~brannon/public/rotation.pdf

# Re: rotation <=> dircos

Phenom

Hi EndZ,

Thanks but not quite. I'm aware of the maths, and the API methods already exist in FEMAP, cf app.feRotationToDirCos. What I want is to use these methods to accelerate a process, but I need to check exactly what the API method does. And so far I can't replicate exactly what it does.

Reading the helpl I thought FEMAP started with rotX, then around the rotated Y, then around the doubly rotated Z. But in that case I would expect the term [3,1] to be sin(2nd rotation) and that's not what is returned by the method...

If a developper has an eye on the code and can indicate what calculation is done I would appreciate it;

Thanks,

AP

# Re: rotation <=> dircos

Phenom

Nevermind I found my mistake: FEMAP thinks in degrees not radians.

So the 1rst order of calculation for the RotationToDirCos method is simply

[1, sin(Rz),-sin(Ry) ; -sin(Rz), 1, sin(Rx) ; sin(Ry), -sin(Rx), 1]