Non-trivial problems with the root persistence for tessellated solids while converting VecGeom shapes.

[Om4143]

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Description

Hi,
I am using VecGeom converter. If I use this converter in same macro that converts gdml to root, works fine but When I export it into root file and convert it again while importing root file, It crashes. This issue is already discussed with @agheata in https://root-forum.cern.ch/t/tessellated-volume-behave-like-box-after-transporting-with-geant-3-and-4-after-converting-cad-to-root-geometry/57083

Attached File:
Macro and required GDML file

void ConvertGDMLtoRootMacro() {  
  TGeoManager* gGeoManager = new TGeoManager("cbmsim", "");
  
  const TString _volumename = "mainframe_02";
  const TString _file = _volumename + ".gdml";
  const TString _file_out = _volumename + ".root";

  TGeoVolume *_vol_assembly = new TGeoVolumeAssembly(_volumename);

  gGeoManager->SetTopVolume(_vol_assembly);
  TGDMLParse parser;
  TGeoVolume *_gdml_vol = parser.GDMLReadFile(_file);
  TObjArray *_node = _gdml_vol->GetNodes();

  Int_t copy_number = 0;
  for (int iNode = 0; iNode < _node->GetEntriesFast(); iNode++) {
    TGeoNode *_fNode = (TGeoNode *)_node->At(iNode);
    TGeoVolume *_fVol = (TGeoVolume *)_fNode->GetVolume();

    _vol_assembly->AddNode(_fVol, copy_number, 0);
    copy_number++;
  }
  _gdml_vol->Draw("ogl");
  gGeoManager->CloseGeometry();
  _vol_assembly->Export(_file_out);
  
       // Convert to VecGeom tessellated solid
   auto converter = TVirtualGeoConverter::Instance(gGeoManager);
   if (!converter) {
      printf("Raytracing a tessellated shape without VecGeom support will just draw a box\n");
   } else {
      converter->ConvertGeometry();
   }    
   _vol_assembly->Draw("ogl");
   _vol_assembly->Raytrace(kTRUE);
   _vol_assembly->RandomPoints(1000000,"");
 
}

Input GDML File:
https://drive.google.com/file/d/1FbQ6rK0fIDXamiAeHWVUxc4M7YcpjA0R/view?usp=sharing

Reproducer

mater branch of ROOT is configured with VecGeom.
run with root -l ConvertGDMLtoRootMacro.C

ROOT version

ROOT 6.31/01

Installation method

build from source

Operating system

Ubuntu 22.04.3 LTS

Additional context

No response

[agheata]

A fix is available in the master branch, @Om4143 can you please confirm that this works for you?

[Om4143]

As I have checked the root file using new development. and converter is working for root file and not seen any persistent problem so far. So In my case, its looks working fine. Thanks a lot 🙏

[Mehul0111]

Why for a small tessellated geometry the message appears

Tile degenerated 2: Length of sides of facet are too small.