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Earth rotation limits in-body image stabilization to 6.3 stops (2020)

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Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#21

Post by t0mas88 »

You don't need GPS to figure out the correction for this. Inertial navigation systems in aircraft (which use very stabilised platforms with a lot of math involved) worked before GPS was available.

It helps to have a rough indication of the current latitude on startup, but you can also figure it out from the gyro outputs. Just takes longer.

With modern sensors (solid state laser gyroscopes) it has all become a lot smaller so if you really want to you can do this in a camera. It's just probably going to be too expensive for what it brings, because 6+ stops of stabilisation is a lot already.

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#23

Post by seszett »

thrdbndndn wrote: post #19
seszett wrote: post #5

Earlier quoted context omitted.

It's explained here: > Your camera, which is using its IBIS system to attempt to keep everything as still as possible, may not realize that you are rotating with your subject and will instead try to zero out any rotation of the camera, including that of the Earth The problem is that the stabilization system tries to compensate for the rotation of Earth (because it can't make the difference between the rotation of Ear…

Why does it stop at Earth's rotation? What about revolution around the Sun?

It also does track the revolution of the Earth around the Sun, and that of the Sun around the Milky Way, as well as the various influences over the Milky Way that make it go less than straight on its way towards the Great Attractor.

Those movements just happen to be slow enough that they don't limit image stabilization to 6.3 stops.

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#24

Post by viraptor »

Euphorbium wrote: post #22
blueflow wrote: post #20

Earlier quoted context omitted.

It doesn't.

Eventually we will have to compensate for gallactic rotation.

I never thought of that one. It's fun to think "we know the whole universe isn't spinning very fast, because our gyros are stable". Feels both obvious and somehow bigger-than-life to me.

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#25

Post by zamalek »

tetris11 wrote: post #3

I still don't quite follow the explanation. The duck and I are on the surface of the same body and are rotating together, maintaining a constant distance... why does Earth rotation need to be corrected for?

In terms of flatland:

Ignore the camera. Instead you have a planet (a circle in flatland), a gyroscope (an arrow that always points in the same direction on the page in flatland), and Mr Square.

        --> [.]
             |
        /----\
        |    |
        \----/
Start off at noon, with Mr Square and the arrow at the top of the planet, the gyroscope to the left of Mr Square pointing at him. Now progress time by 6 hours, by rotating the planet clockwise by 90 degrees. Mr Square and the gyroscope will move with the surface of the planet, resulting in them being on the right side of the circle on the page (the gyroscope above Mr Square on the page). Mr Square's feet will be on the surface of the planet, meaning his rotation matched the planet. However, the gyroscope always points in the same direction on the page. It's now pointing at the sky.

        /----\
        |    | -->
        \----/-[.]
In conclusion: both Mr Square and the gyroscope move with the surface of the planet - in exactly the same way. However, Mr Square will always be standing (along with everything else on the planet), while the gyroscope always points in the same direction on the page (irrespective of the time of day). A camera using the gyroscope would have to account for that.

We wouldn't have the same issue on a (non-rotating) space station. That's why planetary rotation is blamed.

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#26

Post by zamalek »

Euphorbium wrote: post #22
blueflow wrote: post #20

Earlier quoted context omitted.

It doesn't.

Eventually we will have to compensate for gallactic rotation.

We are not kinetically bound to the galactic center, there is no friction causing earth to remain "upright" in respect to the galaxy. Earth is also a freely rotating inertial body and, even though wobbly, it is itself a gyroscope.

The next level of stabilization would probably be gravitational waves.

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#27

Post by crubier »

t0mas88 wrote: post #21

You don't need GPS to figure out the correction for this. Inertial navigation systems in aircraft (which use very stabilised platforms with a lot of math involved) worked before GPS was available. It helps to have a rough indication of the current latitude on startup, but you can also figure it out from the gyro outputs. Just takes longer. With modern sensors (solid state laser gyroscopes) it has all become a lot sma…

Aerospace grade laser gyroscopes are incredibly expensive (and bulky), and even then, they still have massive drift after several hours. If you don't have GPS to relocalize precisely at least every day, there is no way you can know the location of the camera on earth for more than a day, even with state of the art aerospace stuff

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#28

Post by contravariant »

tetris11 wrote: post #3

I still don't quite follow the explanation. The duck and I are on the surface of the same body and are rotating together, maintaining a constant distance... why does Earth rotation need to be corrected for?

Well if it keeps pointing in the exact same direction then it would stay fixed on whatever star it is currently pointing towards.

Which is normally not a problem, but relative to something on the surface of the Earth the stars do move.

So I guess you should ask people to stand directly in front of Polaris if at all possible.

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#29

Post by zamalek »

thrdbndndn wrote: post #19
seszett wrote: post #5

Earlier quoted context omitted.

It's explained here: > Your camera, which is using its IBIS system to attempt to keep everything as still as possible, may not realize that you are rotating with your subject and will instead try to zero out any rotation of the camera, including that of the Earth The problem is that the stabilization system tries to compensate for the rotation of Earth (because it can't make the difference between the rotation of Ear…

Why does it stop at Earth's rotation? What about revolution around the Sun?

Per my other comment: Earth isn't attached to the sun, the sun isn't attached to the galactic center (they are orbiting). They are independent rotational frames of reference. They are also gyroscopes in their own right.

As far as taking pictures of other things on Earth, at least. Taking a picture of another planet/star/galaxy would also face similar challenges.

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#30

Post by Asraelite »

> The first isn’t a good solution for many reasons. Don’t have GPS signal? Shooting next to a magnet? Your system won’t work.

These seem trivial to work around. Just store the last known position and use that. It's rare that you'll be without a GPS signal or beside a magnet, and you certainly won't be traveling long distances in those conditions. And since when do magnets block GPS signals?

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