How to navigate avoiding obstacles using an existing map generating from hector slam?

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Setting the navigation require odometry no ? and just i'm using hector mapping with laser scan . Another question for my real robot I have raspberry pi 3B to interact with stm32 via uart , have to send a caracter to the STM for example "F" to move forword "B" to move back etc...How could i retrieve information from map to go from A to B and how could I use that information to send it via uart ?

You can get odometry from hector mapping, although it is more robust to derive this from your robot wheels (eg. using motor shaft encoders or encoder-free odometry with stepper motors.

To get odomentry from hector, see:

~pub_map_odom_transform (bool, default: true)

Determine if the map->odom transform should be published by the system.

To go from A to B using ROS, the correct approach is to use the Navigation package. To control your robot you will need to implement a node that subscribes to the 'cmd_vel' topic. This node will listen for commands from the Navigation package and respond by generating the "F", "B", etc. accordingly. Sending characters over a UART using Raspberry Pi is very well documented in many places on the internet.

Thank you for answring,moreover i,ll use hector navigation downloading the packgage from git then trying to build a lot of errors appeared for hector_gps_mapping node telling that ceres_catkine not found and then tf not declared