This allows a lot of flexibility in keeping the MVC separate through Angular also keeping the services in Express separate. Front end MVC files are in the static directory and public views. The services and utilities are in the Express directories. So Angular display routes in the config are separate from the Express service routes.
This is how a call is made and data returned to the page:
Express calls the Express utility that deals with that function (processing OpenCV in this case and using a Promise)
Promise is resolved and sent back through the pipeline automagically to the canvas on the page where it is displayed to the user.