Faces from non planar wire and underlying faces - Forum Open Cascade Technology

jerome caucat
Thu, 08/06/2020 - 12:25

Forums:

Hi,

I have a non planar closed wire (made from an arbitrary number of 3D NURBS) and a shape made of faces (that I can sew and use to make a shell), the wire lies on this shape. I want to fill this wire (resulting in a shape made of one or more faces).

I tried to use only the wire by:
* Using BRepBuilderAPI_MakeFace but the wire is not planar.
* Building a surface with GeomPlate_MakeApprox and using BRepBuilderAPI_MakeFace with this surface without success.
* Filling the wire using GeomPlate_BuildPlateSurface and BRepFill_CurveConstraint without success.
* Filling the wire using BRepOffsetAPI_MakeFilling with some success depending on the wire.

I am now trying to use the faces. I am trying two approaches: get the shapes within the wire or cut the shell with the wire. I did not yet succeed, I am not sure I am using the right functions for this.
Could you guide me with the method / functions to use to solve my problem?

Thanks in advance!
Regards

PS: I forgot to mention, I am using version 6.9.1

jerome caucat
Thu, 08/06/2020 - 16:31

I have successfully "drawn" the wire on the shell with BOPAlgo_Builder but now I do not know how to get the faces "inside" the wire.

jerome caucat
Fri, 08/07/2020 - 18:33

I have tried the following method:
* extrude the wire into a prism with BRepPrimAPI_MakePrism
* make it solid with BRepPrimAPI_MakeHalfSpace
* make a shell with the faces of my underlying shape
* use BRepAlgo_Cut to cut the prism from the shell

But the cut does not seem to cut all around the prism.

See attached image:
1. the wire
2. the shape and the wire together
3. the result of the cut

Attachments:

screenshot3.png

jerome caucat
Mon, 08/10/2020 - 12:43

I am able to cut the prism from my previous comment in a plane. Any idea why it does not work correctly in the shell?

jerome caucat
Fri, 08/14/2020 - 18:56

I also try with BRepAlgoAPI_Cut/Common but results vary with the shape of the wire and with the length and orientation of the prism made from the wire. I do not understand what conditions need to be fulfilled for those algorithms to work.

Thomas Anderson
Sat, 08/15/2020 - 16:05

I don't think extruding the wire and boolean operation is the way to go. After the BOPAlgo_Builder operation I would try:

Feed the 2 image shells into bounding box algo and keep the smaller shell.

using ShapeAnalysis_FreeBounds on the 2 image shells, 1 shell(the inner) should have 1 closed wire and the other(the outer) should have 2 closed wires. This assumes that the trimming wire doesn't intersect the original shell's outer wire.

in my gui application, I store the user pick location on the original shell. Then post BOPAlgo_Builder operation, I classify the original pick point on the 2 image shells and keep the shell containing the point.

jerome caucat
Sat, 08/15/2020 - 19:32

Hi Thomas Anderson, thank you for you reply.

How can I get the two image shells you are talking about?

Here is what I have:

// wire: my wire made of a single NURBS3D edge
// shell: my shell made of 11 faces sewn together with BRepOffsetAPI_Sewing and built using BRep_Builder

BOPAlgo_Builder generalFuseBuilder;
generalFuseBuilder.AddArgument(shell);
generalFuseBuilder.AddArgument(wire);
generalFuseBuilder.Perform();
auto fusedShape = generalFuseBuilder.Shape();
// generalFuseBuilder.Images().Size() = 28
// generalFuseBuilder.Splits().Size() = 9
// fusedShape contains 1 compound, 1 shell, 31 faces and 32 wires

auto newShell = (TopExp_Explorer{fusedShape, TopAbs_ShapeEnum::TopAbs_SHELL}).Current();
ShapeAnalysis_FreeBounds safb(newShell);
// safb.GetClosedWires() contains 2 wires

Thomas Anderson
Sat, 08/15/2020 - 23:13

Yes, sorry. I forgot that BOPAlgo_Builder doesn't split apart wires and shells in the result images. This is starting to come back to me. You will have to write a face walking algo that doesn't cross the trimming edges. I am confused that your 1 shell result has 2 closed boundaries. Doing a similar operation here, I get 1 shell result with 1 closed boundary. Maybe you have some bad geometry?

jerome caucat
Mon, 08/17/2020 - 16:20

Actually yes, the sewing operation apparently failed to sew two faces and an inner wire seems to have been created (it can be seen in the screenshots, there is a green line in the middle of the shell).

How can I get the trimming edges generated by BOPAlgo_Builder? I don't understand what is in .images() and .splits().

Thomas Anderson
Tue, 08/18/2020 - 20:13

You have to be careful with sew. It is very liberal in what is acceptable output. Maybe you need to increase the tolerance to get expected results. BOPAlgo_Builder::splits has been removed in occt 7.3 so you probably shouldn't code much around that. TopTools_DataMapOfShapeListOfShape maps a single shape to a list of shapes. so, 'images' maps a single input shape to a list of output shapes and 'origins' maps a single output shape to a list of input shapes. Here is a code clip that dumps out images in a custom program:

    BOPAlgo_Builder bopBuilder;
    for (const auto &s : shapes)
      bopBuilder.AddArgument(s);

    bopBuilder.Perform();
    if (bopBuilder.HasErrors())
    {
      std::ostringstream error;
      error << "error with bopBuilder. error code: "
      << std::endl;
      bopBuilder.DumpErrors(error);
      throw std::runtime_error(error.str());
    }
    
    const TopTools_DataMapOfShapeListOfShape &images = bopBuilder.Images();
    TopTools_DataMapOfShapeListOfShape::Iterator imageIt(images);
    for (int index = 0; imageIt.More(); imageIt.Next(), index++)
    {
      const TopoDS_Shape &key = imageIt.Key();
      std::ostringstream keyBase;
      keyBase << "Output_Images_key_" << formatNumber(index);
      std::ostringstream keyName;
      keyName << keyBase.str() << "_source_shapetype:" << occt::getShapeTypeString(key);
      project->addOCCShape(key, keyName.str());
      
      int count = 0;
      for (const auto &sil : imageIt.Value()) //shape in list
      {
        count++;
        assert(key.ShapeType() == sil.ShapeType());
        
        std::ostringstream mappedName;
        mappedName << keyBase.str() << "_result_shape_" << formatNumber(count);
        
        project->addOCCShape(sil, mappedName.str());
      }
    }

Why don't you post the shapes instead of me guessing what you have from a picture. I am on occt 7.4 so our results might differ.

jerome caucat
Wed, 08/19/2020 - 17:57

Thanks a lot, I managed to find the section wire and test the faces attached to it.