hector mapping before rplidar node?

First of all, thanks for your future answers. Why if I run the rplidar node before the hector_mapping and hector_geotiff launchers I get the error: **[ INFO] [1502821857.396404571]: lookupTransform base_link to laser timed out. Could not transform laser scan into base_frame.** But if I run hector_mapping and hector_geotiff launchers before run the rplidar node everything is fine and I get the map? This is my hector_mapping.launch: thanks,