qspline CC0
qspline (Quaternion Cubic Spline) under the CC0 license
Quaternion Cubic Spline by James McEnnan
Qspline does quaternion interpolation such that the quaternion and angular rate and acceleration vectors are continuous functions of time, while maintaining quaternion normalization.
This project releases the core functions (in qspline.c) under the CC0 license (Public Domain).
The original project can be found here:
http://sourceforge.net/projects/qspline/
The documentation can be found in the original project here:
http://qspline.sourceforge.net/qspline.pdf