code: function fromObject (obj) {
    let polygons = obj.polygons.map(polygonLike => poly3.fromObject(polygonLike))
    let shape3 = fromPolygons(polygons)
    shape3.isCanonicalized = obj.isCanonicalized
    shape3.isRetesselated = obj.isRetesselated
    return shape3
  }
docs: Reconstruct a Shape3 solid from an object with identical property names.
  @param {Object} obj - anonymous object, typically from JSON
  @returns {Shape3} new Shape3 object