code: public void loadScene(final GVRSceneObject model, final GVRResourceVolume volume, final GVRScene scene, final IAssetEvents handler)
      {
          Threads.spawn(new Runnable()
          {
              public void run()
              {
                  AssetRequest assetRequest = new AssetRequest(model, volume, scene, handler, true);
                  String filePath = volume.getFullPath();
                  String ext = filePath.substring(filePath.length() - 3).toLowerCase();
  
                  assetRequest.setImportSettings(GVRImportSettings.getRecommendedSettings());
                  model.setName(assetRequest.getBaseName());
                  try
                  {
                      if (ext.equals("x3d"))
                      {
                          loadX3DModel(assetRequest, model);
                      }
                      else
                      {
                          loadJassimpModel(assetRequest, model);
                      }
                  }
                  catch (IOException ex)
                  {
                      // onModelError is generated in this case
                  }
              }
          });
      }
docs: Loads a hierarchy of scene objects {@link GVRSceneObject} from a 3D model
  replaces the current scene with it.
  <p>
  This function loads the model and its textures asynchronously in the background
  and will return before the model is loaded.
  IAssetEvents are emitted to event listener attached to the context.
  
  @param model
  Scene object to become the root of the loaded model.
  This scene object will be named with the base filename of the loaded asset.
  @param volume
  A GVRResourceVolume based on the asset path to load.
  This volume will be used as the base for loading textures
  and other models contained within the model.
  You can subclass GVRResourceVolume to provide custom IO.
  @param scene
  Scene to be replaced with the model.
  @param handler
  IAssetEvents handler to process asset loading events
  @see #loadModel(GVRSceneObject, GVRResourceVolume, GVRScene)