A polyline is a connected series of line segments. Make fillets by entering a value for the radius. Construct a polyline with the XML code below.
<layercolor>layercolor</layercolor>
and so on
<segment>x;y;radius</segment>
<close>y/n</close>
Name the layer and give the layer a color of your choice.
The polyline has no thickness and is defined by the API by the start and end points of each segment (x,y coordinates) and the associated radius.
Feel free to create a contiguous contour by copying the segment code as much as you want.