// constrain its rotation about shapenormals[i].
var rot1axis = this.unit(this.cross([0,0,1], shapenormals[i]));
var rot1angle = this.angle_between([0,0,1], this.unit(shapenormals[i]));
// constrain its rotation about shapenormals[i].
var rot1axis = this.unit(this.cross([0,0,1], shapenormals[i]));
var rot1angle = this.angle_between([0,0,1], this.unit(shapenormals[i]));