p1.Create(0, 0, 0);
p2.Create(300, 0, 0);
p3.Create(300, 300, 0);
p4.Create(300, 600, 0);
p5.Create(300, 600, -100);
c1.Create(300, 150, 0);
c2.Create(300, 450, 0);
//radius
double radius = 150;
IVector3d zAxis = (IVector3d)(new DSCGEOMCOMLib.Vector3d());
zAxis.Create(0, 0, 1);
//create vertex infos
IVertexInfo vertexInfo1 = (IVertexInfo)(new DSCGEOMCOMLib.vertexInfo());
IVertexInfo vertexInfo2 = (IVertexInfo)(new DSCGEOMCOMLib.vertexInfo());
vertexInfo1.CreateFromCenterAndNormal(radius, c1, zAxis);
zAxis.Multiply(-1);
vertexInfo2.CreateFromCenterAndNormal(radius, c2, zAxis);
//build polyline
IAugPolyline3d polyline = (IAugPolyline3d)(new DSCGEOMCOMLib.AugPolyline3d());
//polyline.AppendVertex(p1);
polyline.AppendNewVertex(p2, vertexInfo1, true);
polyline.AppendNewVertex(p3, vertexInfo2, true);
polyline.AppendVertex(p4);
polyline.AppendVertex(p5);


why p2-p3 arc---->line???