How to display a circle on a Map in a custom manner

This example demonstrates how to create MapPolyline items, which allow displaying circles on a map. The circles' bounds are calculated using different rules:
The EquidistantCircleCreator class allows creating a polyline by calculating the distance from the center point on the Earth surface.
The ScreenCircleCreator class allows creating an polyline by calculating the distance from the center point by using the screen coordinates.
The bounds of the default MapEllipse item are calculated using complex logic that provides an intermediate result. 

The difference of these algorithms is mostly noticeable if a circle with a big radius is displayed close to the poles.