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Show HN: Physically accurate black hole you can put in your room

blackhole.plav.in

11–20 of 204 posts

Re: Show HN: Physically accurate black hole you can put in your room

#11
post #8
post #6

Earlier quoted context omitted.

The app doesn't have to do this itself, phones do it for you. ARCore on Android, ARKit on iOS.

Oh yeah I mean how do the phones do that. I guess it uses dead reckoning with visual cues and some machine learning.

Your phone has an accelerometer, which can be integrated twice to result in slightly accurate dead reckoning; just keep accumulating 3-vectors with every time-slice. That's a helluva lot easier than visual cues.

Re: Show HN: Physically accurate black hole you can put in your room

#12
post #11
post #8

Earlier quoted context omitted.

Oh yeah I mean how do the phones do that. I guess it uses dead reckoning with visual cues and some machine learning.

Your phone has an accelerometer, which can be integrated twice to result in slightly accurate dead reckoning; just keep accumulating 3-vectors with every time-slice. That's a helluva lot easier than visual cues.

"slightly accurate" is the correct description, though -- dead reckoning on a cell-phone-class IMU accumulates drift too quickly to keep objects anchored in space for more than seconds at a time. You need something (visual odometry, SLAM) that provides long-term stability, even if it has short-term noise or poor availability, to fuse in.

Re: Show HN: Physically accurate black hole you can put in your room

#13
post #8
post #6

Earlier quoted context omitted.

The app doesn't have to do this itself, phones do it for you. ARCore on Android, ARKit on iOS.

Oh yeah I mean how do the phones do that. I guess it uses dead reckoning with visual cues and some machine learning.

on iPhone 12 Pro Max and later (maybe only on Pros, I forget) they have a LiDAR sensor built in, allowing for impressively accurate 3D scans of objects with a free app like Scaniverse. But yeah I think AR was the intention there

Re: Show HN: Physically accurate black hole you can put in your room

#14
I remember like 10 years ago when Occulus first came out there was that space simulation demo where you could go around the solar system in VR. You could also "fast travel" by zooming in towards a planet, moon, blackhole.

Yeah, that was the day I learned I have a deep, crippling phobia of large objects. And Melanoheliophobia, which is fear of black holes. The only other time I've felt that way was snorkeling once near a giant 3 story tall bait ball of swirling fish, which was so disorienting and panic inducing that I vomited.

Re: Show HN: Physically accurate black hole you can put in your room

#15
Please correct me if I'm wrong, but it feels like the leading edge of the accretion disk (coming towards the viewer) should be significantly brighter than it is shown here, and the trailing edge (going away from) should be significantly dimmer?

Or could the brightness shown be a result of it being Kerr vs Schwarzschild?

Re: Show HN: Physically accurate black hole you can put in your room

#16
post #14

I remember like 10 years ago when Occulus first came out there was that space simulation demo where you could go around the solar system in VR. You could also "fast travel" by zooming in towards a planet, moon, blackhole. Yeah, that was the day I learned I have a deep, crippling phobia of large objects. And Melanoheliophobia, which is fear of black holes. The only other time I've felt that way was snorkeling once nea…

Same. Especially with circular objects. Placing the black hole in my room using the AR mode was very distressing for me

Re: Show HN: Physically accurate black hole you can put in your room

#17
post #12
post #11

Earlier quoted context omitted.

Your phone has an accelerometer, which can be integrated twice to result in slightly accurate dead reckoning; just keep accumulating 3-vectors with every time-slice. That's a helluva lot easier than visual cues.

"slightly accurate" is the correct description, though -- dead reckoning on a cell-phone-class IMU accumulates drift too quickly to keep objects anchored in space for more than seconds at a time. You need something (visual odometry, SLAM) that provides long-term stability, even if it has short-term noise or poor availability, to fuse in.

When this topic comes up, I'm always happy to share this incredible lecture from many many years ago about sensor fusion and dead reckoning and how you _cannot_ integrate acceleration twice:

https://www.youtube.com/watch?v=C7JQ7Rpwn2k&t=1401s (the whole video is incredible, but this timestamp is the magical bit)

Re: Show HN: Physically accurate black hole you can put in your room

#18
post #14

I remember like 10 years ago when Occulus first came out there was that space simulation demo where you could go around the solar system in VR. You could also "fast travel" by zooming in towards a planet, moon, blackhole. Yeah, that was the day I learned I have a deep, crippling phobia of large objects. And Melanoheliophobia, which is fear of black holes. The only other time I've felt that way was snorkeling once nea…

If somebody feels no fear while zooming towards a black hole, their brain has some strange wires crossed.

Strongly recommend Outer Wilds. Falling into the black hole the first time was one of my most scared moments in gaming. I was totally panicking lol

Re: Show HN: Physically accurate black hole you can put in your room

#19
post #12

Earlier quoted context omitted.

"slightly accurate" is the correct description, though -- dead reckoning on a cell-phone-class IMU accumulates drift too quickly to keep objects anchored in space for more than seconds at a time. You need something (visual odometry, SLAM) that provides long-term stability, even if it has short-term noise or poor availability, to fuse in.

When this topic comes up, I'm always happy to share this incredible lecture from many many years ago about sensor fusion and dead reckoning and how you _cannot_ integrate acceleration twice: https://www.youtube.com/watch?v=C7JQ7Rpwn2k&t=1401s (the whole video is incredible, but this timestamp is the magical bit)

12 years ago I had to write the firmware for an IMU. It took me some real effort to convince my bosses that double integration was, for all practical purposes, impossible. I wish I had known about this video back then...

IMU are very useful to known your orientation though. Even an inaccurate IMU is useful to provide an initial estimate to feed vision-based algorithms.

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