function ParametricGeometry( func, slices, stacks ) {

	Geometry.call( this );

	this.type = 'ParametricGeometry';

	this.parameters = {
		func: func,
		slices: slices,
		stacks: stacks
	};

	this.fromBufferGeometry( new ParametricBufferGeometry( func, slices, stacks ) );
	this.mergeVertices();

}
@author zz85 / https://github.com/zz85
@author Mugen87 / https://github.com/Mugen87

Parametric Surfaces Geometry
based on the brilliant article by @prideout http://prideout.net/blog/?p=44