Degrees of freedom: Difference between revisions
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In mechanics, the number of parameters that can change independently | In mechanics, the number of parameters that can change independently | ||
: e.g. | : e.g. | ||
:: a railcar has one degree of freedom (back and forth) | :: a railcar has one degree of freedom (back and forth). {{comment|(It may round corners and go up hills, but that is not a parameter)}} | ||
:: a regular car could be said to have two you control (translation and rotation) but three that can happen (consider skidding sideways) | :: a regular car could be said to have | ||
:: | ::: two you control (translation and rotation) | ||
:: a | ::: ...but three that ''can happen'' (consider skidding sideways) | ||
:: aircraft have six (roll, pitch, yaw, translation in each direction) | |||
::: e.g. a helicopter, or VTOL will control them | |||
::: while with airplanes you ''hope'' two of those translations ''never'' happen | |||
:: a [[boat]] has six (roll, pitch, yaw, translation in each direction), but you typically don't want more than four | |||
:: though pitch ''happens'' rather than is controllable, or ''does'' much (unless it's a submarine) | |||
:: and usually you want translation only forwards - sideways means capsizing and downwards means sinking | |||
In (electronic) sensors, the same idea amounts to the amount of independently sensed things. They do not have to be related, but when part of a single IC they often are | |||
: a 6DOF motion sensor | Note that | ||
* "can change independently" does not necessarily mean "is actively controllable". | |||
* in a bunch of cases some of these degrees are ''bad'' | |||
In (electronic) sensors, the same idea amounts to the amount of independently ''sensed'' things. | |||
They do not have to be related, but when part of a single IC they often are | |||
: a 6DOF motion sensor might means a 3D accelerometer and 3D gyroscope (but can mean other things!) | |||
: In that context, a 9DOF may well be that plus 3 magnetic field sensors | : In that context, a 9DOF may well be that plus 3 magnetic field sensors | ||
: a lot of different sensors would be 1, 2, or 3DOF. There happen to be fewer that get up to 6 or 9, and they're regularly the above | : a lot of different sensors would be 1, 2, or 3DOF. There happen to be fewer that get up to 6 or 9, and they're regularly the above | ||
Note that they might report more, e.g. some simplified things (amount of acceleration in general), synthesize/filter some more (e.g. figure out where gravity is whenever it's not accelerating) possibly using [[sensor fusion]]. | Note that they might report more, e.g. some simplified things (amount of acceleration in general), synthesize/filter some more (e.g. figure out where gravity is whenever it's not accelerating) possibly using [[sensor fusion]]. | ||
In VR, | |||
: 3DOF might mean rotation only, no movement, | |||
: 6DOF | |||
:: might means rotation and movement as well. | |||
:: or, accelerometer and 3D gyroscope | |||
VR usually has a lot of sensor fusion going on, which blurs the previously-more-1:1 relation between sensors versus sensed things | |||
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In physics and chemistry, | In physics and chemistry, | ||