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Part II. Positioning Chapter 8. Getting Oriented http://www.arcsynthesis.org/gltut/Positioning/Tutorial%2008.html
SPACE - switches between right-multiplying the YPR values to the current orientation and left-multiplying them. W,S - control the outer gimbal. A,D - control the middle gimbal. Q,E - control the inner gimbal.
@author integeruser