draw_geom.C

void draw_geom()
{
	  TEveManager::Create();
   gGeoManager = TGeoManager::Import("Indianflag.root"); // or use TGeoManager::Import(rootfile)
   if (gGeoManager == nullptr) return;
   TEveGeoTopNode *TNod = new TEveGeoTopNode(gGeoManager,gGeoManager->GetTopNode());

   TObjArray* allvolumes = gGeoManager->GetListOfVolumes();
    for(Int_t i=0; i<allvolumes->GetEntries();i++){
          TGeoVolume* vol= (TGeoVolume*)allvolumes->At(i);
          TString volname = vol->GetIconName();
        //  if (volname.Contains("SVTX")) vol->SetLineColor(kRed); 	
        //  else if (volname.Contains("BARR")) vol->SetLineColor(kBlue); 
        //  vol->SetTransparency(20); // set the transparency level for the volumes
  }
  
  gEve->AddGlobalElement(TNod);
  gEve->FullRedraw3D(kTRUE);
 
}