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Re: IDLgrModel, rotation angles [message #38122 is a reply to message #38121]

Mon, 23 February 2004 11:49

James Kuyper
Messages: 425
Registered: March 2000

Senior Member

lyubo wrote:
>
> Hello,
>
> I have a transformation matrix and I must find the amount of rotation
> in degrees. How can I do that? Any help would be appreciated.
>

Forget previous reply; I was being too complicated. A much simpler
expression for the rotation angle in degrees is:

!RADEG*ACOS(0.5D*(TRACE(rot)-1.0D))

Warning: if the rotation angle is small, the trace might exceed 3.0 due
to round-off error; if it's close to 180 degrees, the trace might be
less than -3.0, for the same reason. If you're sure that roundoff is the
only possible cause of such a problem, the following modification avoids
that problem:

!RADEG*ACOS((0.5D*(TRACE(rot)-1.0D)) <1.0 >(-1.0))

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[Message index]

		Re: IDLgrModel, rotation angles By: Rick Towler on Mon, 23 February 2004 11:36
		Re: IDLgrModel, rotation angles By: James Kuyper on Mon, 23 February 2004 11:49
		Re: IDLgrModel, rotation angles By: James Kuyper on Mon, 23 February 2004 10:27

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