When selected  edge, then  how to get points form selected curve edge?

I can get start and end Vertex. But I don't know how to get curve edge of the center point.

Then using center point with start's vertex to get another same distance 2 points.

Could you can give me a hint?

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    swSelectType_e selectionType = (swSelectType_e)selectionMgr.GetSelectedObjectType3(1, -1);

    object entity = (object)selectionMgr.GetSelectedObject6(1, -1);

    switch (selectionType)

    {

         Edge swedge = (Edge)entity;

         Curve swcur = (Curve)swedge.GetCurve();   

         //get start and end vertex

         Vertex startVertex = swedge.GetStartVertex();

         Vertex endVertex = swedge.GetEndVertex();

        //  how to do get another points?  

    }