What exactly is the tf for /fix topic in the tutorial of Hector SLAM

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Thanks for spending your time reading this. I recently went back to Hector SLAM and the origal .bag came with it, the 'Team_Hector_MappingBox_RoboCup_2011_Rescue_Arena.bag'.

In this bag file there seems to be a /fix topic publish the GT from a GPS unit.

Here I have two questions: 1. I can't seem to find the correction tf of this topic as it always displayed incorrectly in my RVIZ. 2. Is the Arena a indoor environment? Is this /fix truly from a GPS or it is just something not meant to be used.