you have to override set_data, for the base case, it will look like this.  If there are more complex transformations performed, such as a ```direction``` field,  look at the annular_wedge renderer.  That renderer actually has some logic in set_data.  


 Eventually, when every renderer has a set_data which calls set_data_new,  I will define set_data on the super class and for simple cases like this remove the set_data implementation on the sub class.