Using an electronic compass for small navigational robot.

I've been building a small navigational robot that (so far crudely) maps it's environment on the fly. To help eliminate drift where the
robots path bends slightly instead of driving straight, I thought I could simply use an electronic compass module and self-correct using a constant heading from the compass.
It has been suggested to me that this would not work as there is too much interference either from the robot itself of for other 'stuff' inside buildings that would render the compass more trouble than it's worth.
Has anyone had experience with this? Is it possible to overcome this? What could be used in place of a compass to get an accurate heading indoors (GPS won't work indoors / is too expensive).
Many thanks, MrQuan
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snipped-for-privacy@gmail.com wrote:

Yes. Some rooms are worse than others. Get a cheap navigational compass and sample readings across the floor (and across your robot). That should give you an idea of the situation.

If its a problem, no. You'd have to map out the magnetic fields throughout the room -- which rather defeats the purpose...

There are some ultrasonic solutions and some optical solutions. Both rely on placing beacons at known locations in the room. Neither is particularly cheap. Many people solve this by using an overhead camera (e.g. robot soccer leagues).
- Daniel
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