gp_Pnt _location = gp_Pnt();
gp_Ax2 _circle_axis(_location, m_axis);
gp_Circ _circle(_circle_axis, m_centerpoint.Distance(m_startpoint));
GC_MakeArcOfCircle _arc(_circle, m_startpoint, alpha_angle, Standard_True);
None of arc built with this function start at the m_startpoint but...