tf odometry and laserscan. Plus Rviz visualisation

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Hi,

I am trying to use rviz to visualise the creation of a 2d map using laserscan and odometry messages.

I have successfully created, published and visualised the odometry message in isolation and laserscan in isolation using rviz. i.e i can see my robot moving along a set path with odometry and i can see my environment (walls etc.) through laserscan message.

What I want to do is link the two together. So that the laserscan message is 'location aware' so instead of just seeing a laserscan at that moment in time, i want rviz to be able to hold the laserscan data points as the robot is travelling in the environment and therefore over time it will build up a 2d map of the whole environment.

I think the way to achieve this is to use the tf message. I have read the tf tutorials but I struggle to fully understand what it is i need to do with the tf message. - What am i transforming? Is it odometry message against laserscan, so tf message frame id = odom and child frame id = laser? -What about the data? Is it purely the odometry message data i already have or do i need to do a calculation? - Do i need to publish all three messages?

Thank you in advance!