What is localization ?

"pogo"

I think I've heard the Northstar name before, and if I'm not mistaken, it is as you guessed a positioning system that tries to emulate how GPS works, but instead of your receiver to acquire signals from different satellites, it acquires signal from emitters distributed accross your environment (on the ceiling for example) on known positions. Be aware, I could be completely wrong on this.

Cheers

Padu

1)the robot explores your house makes a map 2)you turn the robot off, pick him up, and move him to the other side of the house 3)the robot gets turned on again, and told to localize. 4)the robot takes a few scans with his sonar sensors, and compares the local map (what he just scanned) with the global map (the map he's made with previous exploration)

The spot on the global map that has the most similarities to the currect sonar scans is picked as the "I am here" spot on the map.

As the robot roams around, wheel slippage, encoder errors add up over time creating errors in the robots' "I am here" internal variable.

You can calculate the accumulated error, and make the robot localize when the error passes a threshold.

imagine being at a house that you've never been inside, and you have a blind fold. When you first enter the house, you get a quick peek of the layout.

you walk around feeling with your hands (so you don't bump into anything) until you have no clue where you are at. It's time to localize. Pull the blindfold off for a second and take a look where you are at.

You have a map inside your head that you made the first time you peeked. Over time error accumulated in your estimation of your position, and you had to localize... Compare the map inside your head to a scan of the room.

You might be interested to read the following book .... [24MB or so download, BTW] ...

Where am I?" -- Systems and Methods for Mobile Robot Positioning

- dan michaels

======================

Close, but...Northstar is named after the method seafarers used for decades to find their way around the globe: find the North Star, and the position of it and the other stars would tell you (within reason) where you were.

The ER product uses a projector to cast an IR image onto the ceiling, like a planetarium would project constellations. An infrared image sensor looks up to the ceiling, and using the unique shape of the projection indicates both the orientation and position within the room.

Obviously the system needs a ceiling, and a fairly unobstructed view of the ceiling. The robot generally has a better view of the ceiling than walls, so in theory Northstar is better than IR lighthouses positioned around the room.

Similar methods have been devised -- or at least suggested -- by some folks that use the distinct patterns found on most ceilings for localizations. These systems need to be trained. With the right image sensor and image system, it should be possible to detect distinct variations in all but the smoothest, most perfect ceilings. Ceiling with lights and light fixtures, water marks from rain, cracks, weird patterns in the acoustic spray or panels, and other imperfections provide a better rendering subject for the system.

-- Gordon

in mobile robotics, localization refers to the problem of, given a map and sensor readings, determine where you are on the map. similarly, mapping refers to, given sensor readings and exact positions, build a map. neither of these problems are particularly difficult. however, neither of these problems are particularly useful either. what *is* useful is doing them both at the same time, ie, simultaneous localization and mapping (or "slam" as it is generally called). slam is considerably harder than either localization or mapping and is the topic of ongoing research.

chris

Great explanations from everyone! Many thanks!

Thanks! I downloaded it and it looks very interesting so far! JCD