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From "Albert Huang (JIRA)" <j...@apache.org>
Subject [jira] Created: (MATH-363) please clarify quaternion conventions in org.apache.commons.math.geometry.Rotation
Date Sat, 10 Apr 2010 19:52:41 GMT
please clarify quaternion conventions in org.apache.commons.math.geometry.Rotation
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                 Key: MATH-363
                 URL: https://issues.apache.org/jira/browse/MATH-363
             Project: Commons Math
          Issue Type: Improvement
    Affects Versions: 2.0
         Environment: all
            Reporter: Albert Huang
            Priority: Minor


Please clarify which quaternion convention is used in the Rotation documentation, and provide
constructor methods to use alternate quaternion conventions.

For example, the computer graphics community has standardized on representing a rotation of
angle theta about the unit vector (i, j, k)  with the quaternion
{ cos(theta/2), i * sin(theta/2), j * sin(theta/2), k * sin(theta/2) }

e.g., any introductory computer graphics textbook referring to quaternions will describe them
in this convention.  This is also the convention appearing on Mathworld, Wikipedia, etc. 

The convention in org.apache.commons.math.geometry.Rotation instead appears to be
{ cos(-theta/2),  i * sin(-theta/2),  j * sin(-theta/2), k * sin(-theta/2) }

Since I'm not likely to convince you to switch conventions, please at least document the convention
and provide ways to convert from the alternate (this should be trivial?)

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