While this is an area I've typically not found belonging to navigation, this has come up so many times maybe its worth just including it. The goal is to make a node that takes in raw sensor data from a lidar (2D, 3D, I suppose a depth camera, just something that gives ranges in the forward motion direction) and either stop or slow the robot to avoid collisions.

We've added heartbeat server alive + lifecycle transition support and this falls into the same category of safety awareness / promises we can round it off with (e.g. we now know within a timeout everything is running properly and activated, this will now ensure no collisions using raw safety data which nicely rounds off the minimum needs for a safe robot regardless of algorithm for planning and control or localization quality).

In most industrial situations, you might use something like a SICK lidar that has this capability built in and is safety rated. For smaller robots falling under less strict functional safety requirements and budgets, a laser like this may be out of scope and needing a solution based on the ROS sensors they have available. It is not a suitable safety certification alternative, but will give you comparable non-certified capability as long as the sensor and ROS driver are publishing information.

There are 2 major options (probably do both and give the user option of which to use):

• Define a bounding box and a point threshold and if > N points appear in this box in front of the robot, stop it. Usually with a larger bounding box in front of the stop box to warn of a collision and slow the maximum speeds.
• Look at sensor data and look at the closest few points. With the current speed, estimate the time to collision to those points. If the time is < N seconds (1, 5, 10, etc), slow the robot until its = N seconds. The effect here would be to make the robot always N seconds from a collision and continuously scale down the speeds.

This can be trivially made in about a day:

• Transform data from source frame to base_link
• Take in user-generated box sizes
• Check if data in boxes -> react
• Take current odometry speed, do basic kinematics to tell the time to collision. If < N, limit speed.

Useful for both autonomous navigation and as an important element in an assisted teleop system (does this replace the assisted part?)