How would you construct this cylinder?

Hi,

I'm trying to construct a cylinder which shall have one or more of the following attributes:
- elliptical base
- lateral with a certain thickness
- sloped top
- segmented lateral

What would be your approach?

I've tried to construct the latheral and then use BRepOffsetApi_MakeThickSolid. This algorithm fails for certain correct parameter combinations (when the base is very elliptical).

Using BRepOffsetAPI_MakeOffset on base-ellipse or on latheral-face produces no elliptical inner cylinder and even crashes in some parameter combinations, so it's not applicable.

I'd like to avoid boolean operations as they are too slow. A simple cut takes ~1.5sec on my machine - I would need up to 3 cuts per cylinder (sloped top, segmentation, drilling to achieve a thickness).

My current approach is this:
- construct inner and outer base ellipses
- extrude the resulting face via BRepPrimAPI_MakePrism
- apply BRepOffsetAPI_DraftAngle to the top face of the resulting cylinder
But again, this fails in some accurate parameter combinations. (See code below)

As the situation looks a bit hopeless and I already failed constructing a cone with attributes similar to the ones of the cylinder, every hint is very welcome (even for the cone).

I'm using OCC6.3 on Windows.

Code of the last approach to construct a cylinder:
{
// Cylinder's topological data
Standard_Real slopingAngle = 15*PI/180.; // change this to 5 degree to fail
Standard_Real diam = 8; // or change this to 50 to crash
Standard_Real diame = 2;
Standard_Real thick = 0.1;
gp_Pnt bottomCentre(0, -3, 0);
gp_Pnt topCentre(0, 3, 0);
gp_Pnt diameDirectionPoint(1, -3, 0);

gp_Dir diameDirection(gp_Vec(bottomCentre, diameDirectionPoint));

// Construct outer ellipse of bottom
gp_Ax2 bottomSystem(bottomCentre, gp_Dir(gp_Vec(bottomCentre, topCentre)), diameDirection);
gp_Elips bottomEllipse = getEllipse(bottomSystem, diame/2., diam/2.);
BRepBuilderAPI_MakeEdge edgeMaker(bottomEllipse);
BRepBuilderAPI_MakeWire wireMaker(edgeMaker);
BRepBuilderAPI_MakeFace faceMaker(wireMaker);

// Construct inner ellipse of bottom
gp_Elips innerBase = getEllipse(bottomSystem, diame/2.-thick, diam/2.-thick);
BRepBuilderAPI_MakeEdge innerEdge(innerBase);
BRepBuilderAPI_MakeWire innerWire(innerEdge);
faceMaker.Add(innerWire);
TopoDS_Face bottomFace = faceMaker.Face();

// Extrude base to top
gp_Vec extrusionVector(bottomCentre, topCentre);
BRepPrimAPI_MakePrism prismMaker(bottomFace, extrusionVector);
TopoDS_Shape cylinder = prismMaker.Shape();

//
// Slope top
//
BRepOffsetAPI_DraftAngle draftAngle(cylinder);

// determine upper face
TopExp_Explorer ex;
TopoDS_Face upperFace;
for (ex.Init(cylinder, TopAbs_FACE); ex.More(); ex.Next())
{
// The upper face is the last one. (Admitted, this might be optimized :)
upperFace = TopoDS::Face(ex.Current());
}

gp_Pln neutralPlane = gp_Pln(topCentre, diameDirection);
gp_Dir removalDirection = diameDirection;
Standard_Real rotationAngle = slopingAngle;

// slope top to other direction
if(slopingAngle {
Standard_Real neutralPlaneAngle = PI;
neutralPlane.Mirror(p2);
removalDirection = removalDirection.Reversed();
rotationAngle = -slopingAngle;
}

draftAngle.Add(upperFace, removalDirection, rotationAngle, neutralPlane, 0);
draftAngle.Build();
cylinder = draftAngle.Shape();
}

gp_Elips TopoFeatureElliptical::getEllipse(const gp_Ax2& system, Standard_Real radius1, Standard_Real radius2)
{
if(radius1 {
gp_Elips ellipse(system, radius2, radius1);
ellipse.Rotate(system.Axis(), PI*90/180);
return ellipse;
}
gp_Elips ellipse(system, radius1, radius2);
return ellipse;
}