AMCL Time-based updating

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For it to work most effectively, AMCL requires new information from each lidar scan it ingests. If the robot is not moving, feeding AMCL the same scan over and over will make the algorithm perform much worse.

AMCL is designed to handle Global Localization for difficult cases: imagine multiple identical rooms, each with a doorway to a shared hallway. If the robot is inside one of the rooms, there is no way to determine which room it's in from just the lidar scans - the robot will have to move into the hallway to determine a single solution. This is why AMCL wants "new" scans.

AMCL has a service for updating on command.

request_nomotion_update (std_srvs/Empty)

Service to manually perform update and publish updated particles.

So setup a timer and request the service periodically.

Not out of the box, but if you read the AMCL code, I think you'll find it pretty simple to change those criteria.

Why _not_ do it? Imagine your robot is just hanging out for a few hours, scan matcher and the lasers aren't perfect, you'll end up drifiting in place while staying still I imagine. Also, if you're running a robot at let's say conservatively 0.5m/s, you're probably going to trigger your AMCL config once a second typically (more or less, I'm just looking at defaults). Do you really want to run this more than once a second?