Conical surface - Forum Open Cascade Technology

Ivan Poberezhnyk
Sat, 11/22/2025 - 01:30

Forums:

I'm trying to make a conical surface bounded by two lines and a circular arc. Here is a sample code

double h = 20.0;
double a = 60.0 * (M_PI / 180.0);
double dh = h * tan(a / 1.0);
double r = dh;

gp_Dir aDir(0.0, 0.0, 1.0);

gp_Pnt aPnt0(0.0,           0,              0.0          );
gp_Pnt aPnt1(dh,            0,              aPnt0.Z() + h);
gp_Pnt aPnt2(0,             dh,             aPnt0.Z() + h);

//
gp_Circ circ(gp_Ax2(gp_Pnt(0.0, 0.0, aPnt0.Z() + h), aDir, gp_Dir(1.0, 0.0, 0.0)), r);
Handle(Geom_TrimmedCurve) aArc = GC_MakeArcOfCircle(circ, aPnt1, aPnt2, true);
Handle(Geom_TrimmedCurve) aSeg0 = GC_MakeSegment(aPnt0, aPnt1);
Handle(Geom_TrimmedCurve) aSeg1 = GC_MakeSegment(aPnt2, aPnt0);
// Wire
TopoDS_Edge anEdge1 = BRepBuilderAPI_MakeEdge(aSeg0);
TopoDS_Edge anEdge2 = BRepBuilderAPI_MakeEdge(aArc);
TopoDS_Edge anEdge3 = BRepBuilderAPI_MakeEdge(aSeg1);
TopoDS_Wire aWire  = BRepBuilderAPI_MakeWire(anEdge1, anEdge2, anEdge3);
// Surface
GC_MakeConicalSurface coneMaker(gp_Ax2(aPnt0, aDir, gp_Dir(1.0, 0.0, 0.0)), a, 0.0);
Handle(Geom_ConicalSurface) aCone = coneMaker.Value();
// Face
BRep_Builder B;
B.MakeFace(m_Shape, aCone, 0.001);
BRepLib_MakeFace faceMaker(m_Shape);
faceMaker.Add(aWire);
m_Shape = faceMaker.Face();

Result of rendering this m_Shape shown in the first attached screenshot.

Adding

Handle(ShapeFix_Face) aFixShape = new ShapeFix_Face(m_Shape);
if (aFixShape->Perform())
{
    m_Shape = aFixShape->Face();
}

does not help much. See the second screenshot.

What am I doing wrong?

P.S. Green lines with arrows are just my visualization of the edges.

Attachments:

cone_no_fix.png

cone_with_fix.png

Dmitrii Pasukhin
Sat, 11/22/2025 - 01:47

Hello, the topology is not valid. The wire need to organise circle and also you need to add 2d curve (pcurve, 2d curve, seam edge).

The most comfortable example with demo: https://dev.opencascade.org/content/sample-cylinder-order-edges-wire

Working sample: https://dev.opencascade.org/content/splitting-edge-cylinder

My overall recommendation - try to work with OCCT's Draw command and play with topology and geometry to get the understanding of the topology.

Best regards, Dmitrii.

Ivan Poberezhnyk
Sat, 11/22/2025 - 03:35

Thanks for the quick reply. My wire does form a circle: line (p0, p1), an arc (p1, p2), and the second line (p2, p0). As for the pcurves - my bad, it is not my real code, just a code snippet where I'm trying to understand issues I have with cones. I modified the code to add pcurves to each edge using projection (should be enough for the POC), like this:

ShapeAnalysis_Edge sae;
Handle(ShapeConstruct_ProjectCurveOnSurface) project = new ShapeConstruct_ProjectCurveOnSurface;
project->SetPrecision(tolerance);
project->Init(aCone, tolerance);
{
    TopoDS_Vertex V1 = sae.FirstVertex(anEdge1);
    TopoDS_Vertex V2 = sae.LastVertex(anEdge1);
    B.UpdateVertex(V1, tolerance);
    B.UpdateVertex(V2, tolerance);
    Handle(Geom2d_Curve) c2d;
    project->Perform(aSeg0, aSeg0->FirstParameter(), aSeg0->LastParameter(), c2d);
    B.UpdateEdge(anEdge1, c2d, aCone, TopLoc_Location(), tolerance);
}

And the same for the two other edges. I have also set the wire orientation to TopAbs_REVERSED. Now the code is rendered, and it shows the same issue I have in my main code - the pure quality of the cone, shown in the screenshots.

Attachments:

cone1.png

cone2.png

cone3.png