
Robot Localization in Maze Using Particle Filter - keyboardman
https://github.com/leimao/Particle_Filter
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guessmyname
Previous thread →
[https://news.ycombinator.com/item?id=21862060](https://news.ycombinator.com/item?id=21862060)

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Xophmeister
This comment[1] made it clear to me what exactly was going on. Also, on the
author's GitHub, there's a link to a similar project,[2] which runs
interactively in a browser, making the concept a bit more accessible.

Imagine you were dropped into a familiar setting, but were blindfolded. You
know this place literally like the back of your hand, but you're only allowed
to observe your location in a very limited sense -- say, every 10 seconds, you
can reach out in the four cardinal directions to feel what, if anything, is
around you -- but you can otherwise move around freely. Given enough
observations, you can slowly establish your location precisely.

What was bugging me is the use of a maze. Mazes are meant to be "solved" and
this doesn't solve the maze -- in the sense of reaching a goal point -- but
rather only allows the robot to localise itself within it. Given that the
robot necessarily has an internalisation of the maze (a map), it might have
been nice to see it simultaneously solve it, while getting its bearings,
rather than just wiggling about, seemingly at random.

[1]
[https://news.ycombinator.com/item?id=21878928](https://news.ycombinator.com/item?id=21878928)

[2]
[http://www.claudeonthe.net/ai/particle_filter/particle_filte...](http://www.claudeonthe.net/ai/particle_filter/particle_filter.html)

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lawlessone
I'm sure this is something cool but i don't understand it.

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IanCal
The problem that's being solved here is "I'm somewhere in a building, a
building I know the exact layout of. Where am I in the building?".

The robot in this case can ask "roughly how far away is the wall in front of
me, to the sides of me and behind me". Given that information it can rule out
some places it might be, and figure out some more likely places. Then it moves
a bit somewhere and says "OK, _now_ how far away are the walls?".

You could imagine doing this in your house, blindfolded. You reach out and
touch a wall in front of you - ok you know you are not in the middle of a room
unless it's a small room. There's no wall to the sides of you reachable so
you're not in a corner. You keep moving and measuring and you can work out
where you probably are. If the walls either side of you and straight in front
of you are far away, then you step forwards and the walls either side are
suddenly touchable, you know you've just crossed from a room into a corridor.
There's only one place in my house personally that can happen so I'd be able
to say exactly where I was if that happened.

This is localisation. There's a harder problem called SLAM (simultaneous
localisation and mapping) where you don't know what the world looks like or
where you are and are trying to build up a model of the world and where you
are in it.

