message: const attribute get tsdf map from server
diff: @@ -95,7 +95,7 @@ class TsdfServer {
  void updateMeshEvent(const ros::TimerEvent& event);
  void publishMapEvent(const ros::TimerEvent& event);
  - std::shared_ptr<TsdfMap> getTsdfMapPtr() { return tsdf_map_; }
  + std::shared_ptr<TsdfMap> getTsdfMapPtr() const { return tsdf_map_; };
  /// Accessors for setting and getting parameters.
  double getSliceLevel() const { return slice_level_; }
  