function interpolate( p0, p1, p2, p3, t, t2, t3 ) {

		var v0 = ( p2 - p0 ) * 0.5,
			v1 = ( p3 - p1 ) * 0.5;

		return ( 2 * ( p1 - p2 ) + v0 + v1 ) * t3 + ( - 3 * ( p1 - p2 ) - 2 * v0 - v1 ) * t2 + v0 * t + p1;

	}
Spline from Tween.js, slightly optimized (and trashed)
http://sole.github.com/tween.js/examples/05_spline.html

@author mrdoob / http://mrdoob.com/
@author alteredq / http://alteredqualia.com/