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,

Commenter-1.

Thank you for reply!

Hello,

In this case we need more information.

Please attache a step file or created .xbf document. You can save your document using next code:

anApp->SaveAs(aDoc, "D:/test.xbf);

Best regards,

Commenter-1.

Thanks.
I have solved it. It's my fault.

Hello Dear Author, how did you manage to do it, I have the same problem. Can you share your experience?

Hello, can you describe your problem?

Best regards, Commenter-1.

Thanks for the reply Dmitrii.
I want to convert STEP to OBJ and when I try to do
aWriter.Perform(aDoc, aFileInfo, progress->Start())
Return "No mesh data to save."

Please check my first response on this topic with code sample.

Do you do the same? Before writing you need to generate mesh to write. You can use commercial EMesh or public IncrementalMesh

Best regards, Commenter-1.

I do as you described, I use BRepMesh_IncrementalMesh while creating a STEP file, after which I use
const writer = new oc.STEPControl_Writer();
writer.Transfer()
writer.Write("test.step" )
then I use
const theStepReader = new oc.STEPCAFControl_Reader();
theStepReader.Transfer(aDoc);
then I create aWriter
const aWriter = new oc.RWObj_CafWriter(fileName);
aWriter.Perform(aDoc, aFileInfo);

I have only presented here the main steps that I take.

To export to the STEP format you don't need to make tessellation.

You need to call BRepMesh_IncrementalMesh before export to Obj. You need to tesslated result of STEPCAFControl_Reader.

Best regards, Commenter-1.

I got it all. Thanks a lot

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!

I found out only one problem - creating  null handle of progress. Default constructore create NULL object, null object don't be able to have ->Start() method.

You need to use operator new for creating "Handle" objects.

>> Handle(Message_ProgressIndicator) progress = Handle(Message_ProgressIndicator)();

Best regards, Commenter-1.

Thanks Dmitrii,

My source code exited this constructor (my code is not clean so it hard reviewing a bit). I have compared very carefully your suggestions code but I did not find what I was missing.

RWMesh_CoordinateSystem aSystemCoordSys = RWMesh_CoordinateSystem_Zup, aFileCoordSys = RWMesh_CoordinateSystem_Yup;

Handle(Message_ProgressIndicator) progress = Handle(Message_ProgressIndicator)();

TColStd_IndexedDataMapOfStringString aFileInfo;

Please lets me know if you have any comment to help me resolve this issue.

Thanks.

I don't give you any code. I just spot the error.

You need to use "new" to create a Handle.

Handle(Message_ProgressIndicator) progress = new Message_ProgressIndicator();

Best regards, Commenter-1.

Thanks Dmitrii,

Sorry I don't understand your meaning correctly.
I have tried your suggestion, but I see Message_ProgressIndicator constructor is protected.
Please lets me know if you have any information.
BTW,I am concerning about my function is written in CLI/C++ class. I wrapper source code to use in C# project.

Thanks.

Oh, Sorry, Which version do you use?

bool RWObj_CafWriter::Perform (const Handle(TDocStd_Document)& theDocument,
                               const TColStd_IndexedDataMapOfStringString& theFileInfo,
                               const Message_ProgressRange& theProgress)

the last parameter as a stack object. You need to create a default object by default constructor. Why do you use Handle?

If you don't want to use progress indicator you should use the next code:

aWriter.Perform(aDoc, aFileInfo, Message_ProgressRange());

Best regards, Commenter-1.

Thanks Dmitrii, I change source as your suggestion

Message_ProgressRange theProgress;
aWriter.Perform(aDoc, aFileInfo, theProgress);

Then it worked.  I am working on 7.7.0 version

Why do you use Handle?

I have newbie with this platform so I copied source code from other guy to check result first.

BTW, As I know after export to Obj then we have got two files : one is *.obj and other is .mtl (material). But I see my result just only one file.

Please lets me know if you have comment for this one.

Thanks.

Creating of ".mtl" file calls only if one or more of your faces have FaceColour or (Material AND UV-points)

Best regards, Commenter-1.

Commenter-3 wrote:

BTW, As I know after export to Obj then we have got two files : one is *.obj and other is .mtl (material). But I see my result just only one file.

Material file is created when document has materials / colors assigned to shapes. Try this workflow on a STEP file that defines some colors.

Thanks gkv311 and Dmitrii,

Today, I have tried new challenge is load Step file by Unity directory (don't via *.obj file).
I have read and known Unity3D rendering base on the Mesh that includes Vertex and Normal and triangles.
So, I have tried use the above way to read Step file then looking for way to get above information then put to Unity.
However, I didn't see any sample code to get Vertex and Normal and triangles information from step file.
Please lets me know if you have any information about this one!
Thanks.

From step file directly it is complex with just OCCT. But you be able to exctact Poly_Triangulation from TopoDS_Face as a part of OCCT model imported from STEP file.

There a lot of samples for that. You can look into, for example, RWObj_Writer to understand how to work with mesh from OCCT data model.

Best regards, Commenter-1.

Hello everyone,

I'm working on a C++/CLI wrapper that reads a STEP file and exports it to the OBJ format using OCCT (OpenCascade 7.7.0). My goal is to generate a separate mesh/group in the OBJ file for each SOLID found in the STEP file.

So far, the code works and produces a single OBJ file using RWObj_CafWriter, but the result is a single combined mesh, even though I try to add each solid as a separate shape in the XCAF document.

Here is the relevant part of my code:

Handle(XCAFDoc_ShapeTool) shapeTool = XCAFDoc_DocumentTool::ShapeTool(doc->Main());
TDF_LabelSequence rootLabels;
shapeTool->GetFreeShapes(rootLabels);

for (TDF_LabelSequence::Iterator it(rootLabels); it.More(); it.Next())
{
const TDF_Label& rootLabel = it.Value();
TopoDS_Shape rootShape;
if (!XCAFDoc_ShapeTool::GetShape(rootLabel, rootShape))
continue;

for (TopExp_Explorer exp(rootShape, TopAbs_SOLID); exp.More(); exp.Next())
{
    const TopoDS_Shape& subShape = exp.Current();

    // Add to document
    TDF_Label subLabel = shapeTool->NewShape();
    shapeTool->SetShape(subLabel, subShape);

    BRepMesh_IncrementalMesh mesher(subShape, 0.1, Standard_True);
    ++shapeCount;
}
}

Finally, I export with:

RWObj_CafWriter writer(nativeObjPath.c_str());
writer.Perform(doc, theFileInfo, Message_ProgressRange());

Despite this, the OBJ contains just one group/object.

My question:
How can I make sure each solid appears as a separate mesh/group in the OBJ output? Is there a recommended way to organize the document or assign attributes to enable this?

Thank you very much in advance!

Best regards, Commenter-5

Update:
The issue was that I didn't assign a name to each TDF_Label created for the sub-shapes.
RWObj_CafWriter uses these names to distinguish objects in the OBJ file.

Adding these lines fixed it:

std::string name = "Part_" + std::to_string(shapeSOLIDCount);
TDataStd_Name::Set(subLabel, TCollection_ExtendedString(name.c_str()));

Now each solid is correctly exported as a separate OBJ object.

I have implemented it in my application. You can find it here: https://github.com/sharjith/ModelViewer-Qt
You can use the methods to adopt to your cli application. Let me know if you have any questions.