Allow loading of only geometry, or only volume.

offline_ray_tracer/source/main.cpp

@@ -85,7 +85,9 @@ std::int32_t main(std::int32_t argc, char** argv)
     {
       std::cout << "Loading slice " << slice << ".\n";
       last_slice = slice;
+      if (!settings.data_filepaths[slice].geometry.empty())
         pd_mapper->SetInputData(rt::poly_data_io        ::read(settings.data_filepaths[slice].geometry));
+      if (!settings.data_filepaths[slice].volume  .empty())
         ug_mapper->SetInputData(rt::unstructured_grid_io::read(settings.data_filepaths[slice].volume  ));
     }