step file conversion obj example

Hello.

Obj writer work only with Mesh. That is why you need to create mesh for imported document. Step format work with BRep and Mesh. I think only BRep exists in your file.

For more detailed help, tell me which version or branch of OCCT you are using. Additionally, please attach the STEP file.

To update a document to create a mesh you can use:

  TDF_LabelSequence aRootLabels;
  myDoc.ShapeTool()->GetFreeShapes (aRootLabels);

  TopoDS_Compound aCompound;
  BRep_Builder    aBuildTool;
  aBuildTool.MakeCompound (aCompound);
  for (TDF_LabelSequence::Iterator aLabIter (aRootLabels); aLabIter.More(); aLabIter.Next())
  {
    TopoDS_Shape     aShape;
    const TDF_Label& aLabel = aLabIter.Value();
    if (XCAFDoc_ShapeTool::GetShape (aLabel, aShape))
    {
      aBuildTool.Add (aCompound, aShape);
    }
  }

  Bnd_Box aBndBox;
  BRepBndLib::Add (aCompound, aBndBox, Standard_False);
  if (aBndBox.IsVoid())
  {
    return false;
  }

  NCollection_Vec3<double> aMin, aMax;
  aBndBox.Get (aMin.x(), aMin.y(), aMin.z(), aMax.x(), aMax.y(), aMax.z());
  const NCollection_Vec3<double> aBndDelta = aMax - aMin;

  BRepMesh_IncrementalMesh anAlgo;
  anAlgo.ChangeParameters().Deflection = aBndDelta.maxComp() * myLinearDeflection * 4.0;
  anAlgo.ChangeParameters().Angle      = myAngularDeflection;
  anAlgo.ChangeParameters().InParallel = Standard_True;
  anAlgo.SetShape (aCompound);
  anAlgo.Perform();

Best regards,

Dmitrii.

Handle(TDocStd_Document) aDoc;
    
Handle(TDocStd_Application) anApp = DDocStd::GetApplication();
anApp->NewDocument(TCollection_ExtendedString("BinXCAF"), aDoc);
STEPCAFControl_Reader theStepReader;
    theStepReader.SetColorMode(true);
    theStepReader.SetNameMode(true);
    IFSelect_ReturnStatus status = theStepReader.ReadFile(theFileName.ToCString());
if (status == IFSelect_RetDone )
    {
      bool isFailsonly = false;
      //aReader.PrintCheckLoad( isFailsonly, IFSelect_ItemsByEntity );

      //int aNbRoot = aReader.NbRootsForTransfer();
      //aReader.PrintCheckTransfer( isFailsonly, IFSelect_ItemsByEntity );

      //aReader.TransferEntity(aDoc);

      theStepReader.Transfer(aDoc);

      TDF_LabelSequence aRootLabels;
      Handle(XCAFDoc_ShapeTool) Assembly = XCAFDoc_DocumentTool::ShapeTool(aDoc->Main());
      //myDoc->ShapeTool()->GetFreeShapes(aRootLabels);
      
      Assembly->GetFreeShapes(aRootLabels);

      TopoDS_Compound aCompound;
      BRep_Builder    aBuildTool;
      aBuildTool.MakeCompound(aCompound);
      for (TDF_LabelSequence::Iterator aLabIter(aRootLabels); aLabIter.More(); aLabIter.Next())
      {
          TopoDS_Shape     aShape;
          const TDF_Label& aLabel = aLabIter.Value();
          if (XCAFDoc_ShapeTool::GetShape(aLabel, aShape))
          {
              BRepMesh_IncrementalMesh(aShape, 0.01).Perform();
              //aBuildTool.Add(aCompound, aShape);
          }
      }

Standard_Real aFileUnitFactor = 1.0;
      RWMesh_CoordinateSystem aSystemCoordSys = RWMesh_CoordinateSystem_Zup, aFileCoordSys = RWMesh_CoordinateSystem_Yup;
      Handle(Message_ProgressIndicator) progress = Handle(Message_ProgressIndicator)();

      TColStd_IndexedDataMapOfStringString aFileInfo;



      aFileInfo.Add("Author", "sky");
      const Standard_Real aSystemUnitFactor = UnitsMethods::GetCasCadeLengthUnit() * 0.001;
      RWObj_CafWriter aWriter(TCollection_AsciiString("test.obj"));
      aWriter.ChangeCoordinateSystemConverter().SetInputLengthUnit(aSystemUnitFactor);
      aWriter.ChangeCoordinateSystemConverter().SetInputCoordinateSystem(aSystemCoordSys);
      aWriter.ChangeCoordinateSystemConverter().SetOutputLengthUnit(aFileUnitFactor);
      aWriter.ChangeCoordinateSystemConverter().SetOutputCoordinateSystem(aFileCoordSys);
      aWriter.Perform(aDoc, aFileInfo, progress->Start());

I am working on 7.7.0 version. And my application is crash  at aWrite.Perform(). Please review and lets me know my fault.

Thanks!