[MATH-363] please clarify quaternion conventions in org.apache.commons.math.geometry.Rotation

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 2.0

Environment

all

• Assignee: Unassigned
• Reporter: Albert Huang
• Created: 10/Apr/10 19:51
• Updated: 23/Mar/11 20:02
• Resolved: 11/Apr/10 12:03

Description

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?)