I just realized that we don't need a scratch variable because `this._ti` needs to be a new `Cartesian3`. I would change it to something like:
```javascript
var ti = this._ti = new Cartesian3();
Cartesian3.multiplyByScalar(controlePoint1, 2.0, ti);
Cartesian3.subtract(ti, controlPoint2, ti);
// ...
```
I think that would be more readable and looks a lot like the prototype chaining.