Slam gmapping and hector

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Hello!

I'm currently trying to implement a slam using gazebo.

I already have the laser tf publish, as well and the tf between the wheels and the base_link and gazebo publishes the odometry and I think it publishes the tf too.

So i'll put up the questions in order:

1- Why is the map so horrible using gmapping and it's fairly good using hector-slam?

2- My current tf tree using hector is this : Do I need the transforme between odom->base_footprint->base_link for slam-gmapping to work and why would I need it either way?

3-I don't really understand how the odom tf is published. I used the robot_state_publisher node and I know it publishes the wheels tf but does it also publish the odom tf or is it gazebo who does it?

Thanks in advance!