how does laserscan data match the map

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This problem has been researched for decades, and no single best solution has been found. As a start, you could look at http://wiki.ros.org/laser_scan_matcher and read the Andreas Censi paper mentioned there.

Since your question is a little broad, I will make the assumption you already know how 2D lidar works, if you want to understand how this is done in code to convert into a map, I suggest you review the velodyne repo: https://github.com/ros-drivers/velodyne

In there you will see how this is done, take a look at to start with and work your way how this is converted into an image data:

https://github.com/ros-drivers/velody... https://github.com/ros-drivers/velody...