Hacker News Reader

Comment by lm2s | Hacker News Reader

In regard to the compass aspect, why would the compass work mostly everywhere? Indoor is not a problem for the earth magnetic field, nor is a airplane.. The GPS not working everywhere (specially indoors) makes sense: it can't receive the satellites signals. But a compass is made with a magnetometer which works indoors and in airplanes, etc. Only problems will be in the poles and near objects producing strong magnetic fields..

View on HN

Yeah I though about that when writing it. I don't know.

What I do know is I used to wear a Tissot T-Touch which has a compass, and it doesn't work everywhere. Not in underground car parks, and certainly not on airplanes.

Maybe it's specific to the Tissot, I'm not sure.

Maybe they are using GPS as a compass?

This. Many mobile, or even vehicle (GPS) compasses are not magnetic at all, but are doing point to point math on your GPS coordinates to "determine" your compass heading.

A compass is influenced by anything that disturbs the local magnetic field: magnets, metal objects, electrical currents, etc.

> and near objects producing strong magnetic fields.

Or any ferrous material that distorts magnetic fields locally, such as steel beams, rebar in concrete, electric cables, etc. You can map an office building by measuring the local magnetic field distortion.

Compass everywhere sounds easy until you try it.

The magnetometer is always recalibrating itself, so changes to the local magnetic field can be cancelled out.

How? Sensor fusion with a gyroscope will help transient problems, like walking past some iron rebar, but would have to drift back to the magnetometer's reading if in a long-term situation. Using the GPS as a compass is pretty sketchy, too, AFAIK. Is there some smarter trick?

Reply on news.ycombinator.com