Get the localization track of hector_mapping

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I want to use the localization part of hector_mapping, so I want to test the accuracy of the localization. I am going to set a straight physical track for the robot, so the path of the robot is a very straight line. Then I want to get the hector_mapping localization trajectory(a track containing all the localization points), and then compare the actual trajectory with the hector_mapping locating trajectory. How can I get the the above track measured by hector_mapping? Or is there a better way to test the localization accuracy of hector_mapping?