Is 6D GPS useful?

I don't have a 6D, so I have no idea how well its GPS works.  But, chances are it uses the same type of GPS chips in smartphones, etc.

In general, GPS does not work indoor, unless the building is a wood frame house like most in the U.S.  The signal is relatively weak.  New satellites have stronger transmitters.  At the replacement rate of 1 or 2 a year, the upgrade cycle is over a decade.

It works great in flat area with no tall building blocking the signal.  The worst is when you get multi-path.  You can be inside a building but near a window.  The receiver can see less than half the sky.  If there is a tall building across the street reflecting signals from satellites blocked by your roof, then this is call multi-path.  The receiver would think those satellite are further away than they really are.  The calculated position may put you on the other side of the tall building.  Some times, the position may be off by a block.

Another type of error comes from the assumption that you are traveling on a straight line.  Most GPS chips were designed for vehicle navigation.  If you are wandering around or standing still, the accuracy drops.

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Peter Kwok
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