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

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