3 ms·

Does anyone have a more ELI5 explanation?

by gurumeditations 7y ago

AceJohnny2 7y ago
My guess: echolocation, but with electromagnetic waves (light) rather than sound waves
- airstrike 7y ago
  Makes me wonder if the results of this test could be improved by layering in sound waves for additional resolution
  - cjhanks 7y ago
    Soundwave SnR deteriorates much faster than lightwave. That said, there are companies uses sound for generating maps.
  - nixpulvis 7y ago
    Why not use other frequencies of the EM spectrum, some that say penetrate walls? I've heard of WiFi being used to 3D map buildings for example.
    - adamnemecek 7y ago
      My guess is that it doesn't create the echo.
3JPLW 7y ago
This site — which appears to be the source data for OP as well — has some really nice visualizations. It looks like it's more a scan than a flash, combined with extraordinarily fast frame rates to precisely measure the light's travel time and allow for reconstruction. http://www.computationalimaging.org/publications/nlos-fk/ http://www.computationalimaging.org/publications/nlos-fk/
cjhanks 7y ago
When the light bounces off of the target surface it scatters. The light which bounces back to the sensor array has time offsets depending on the geometry of the scene, those can be modeled as curves. Similar (in that it's the inverse case) to a bucket of water, if you drop something in it, it creates rippled waves. If you only observe the ripples in the bucket, you can reasonably derive where the thing was likely dropped.
- zimpenfish 7y ago
  > If you only observe the ripples in the bucket, you can reasonably derive where the thing was likely dropped. Akin to the Polynesian wave navigation using stick charts: http://thenonist.com/index.php/thenonist/permalink/stick_charts/ http://thenonist.com/index.php/thenonist/permalink/stick_cha...
um_ya 7y ago
Imagine turning a wall into a mirror. Essentially, it uses a laser beam and fancy math to see around a corner, similar to looking at a mirror.
GistNoesis 7y ago
Imagine you have a cave the ceiling of which is covered by a thin film of water. At t=0, there is an explosion which shakes the water and make it fall vertically to the ground as droplets. You have a grid of water detectors on the grounds, which can tell you where and when a droplet hit the floor. If at t1 you detect a drop of water at floor coordinates (x,y), you know the height of the ceiling at (x,y) is h1 which you can compute from t1. So you can make an image of the ceiling. The paper algorithm is a fancier version of this, where the droplets are not falling straight down to the floor, but spread out like sphere ripples. So you need some fft math to deconvolve. The added benefit of using waves, is that you can see behind the objects, and you have a real 3D and not a 2.5D image.

Does anyone have a more ELI5 explanation?

AceJohnny2 7y ago

My guess: echolocation, but with electromagnetic waves (light) rather than sound waves

airstrike 7y ago
Makes me wonder if the results of this test could be improved by layering in sound waves for additional resolution
- cjhanks 7y ago
  Soundwave SnR deteriorates much faster than lightwave. That said, there are companies uses sound for generating maps.
- nixpulvis 7y ago
  Why not use other frequencies of the EM spectrum, some that say penetrate walls? I've heard of WiFi being used to 3D map buildings for example.
  - adamnemecek 7y ago
    My guess is that it doesn't create the echo.

3JPLW 7y ago

This site — which appears to be the source data for OP as well — has some really nice visualizations. It looks like it's more a scan than a flash, combined with extraordinarily fast frame rates to precisely measure the light's travel time and allow for reconstruction. http://www.computationalimaging.org/publications/nlos-fk/ http://www.computationalimaging.org/publications/nlos-fk/

cjhanks 7y ago

When the light bounces off of the target surface it scatters. The light which bounces back to the sensor array has time offsets depending on the geometry of the scene, those can be modeled as curves. Similar (in that it's the inverse case) to a bucket of water, if you drop something in it, it creates rippled waves. If you only observe the ripples in the bucket, you can reasonably derive where the thing was likely dropped.

zimpenfish 7y ago
> If you only observe the ripples in the bucket, you can reasonably derive where the thing was likely dropped. Akin to the Polynesian wave navigation using stick charts: http://thenonist.com/index.php/thenonist/permalink/stick_charts/ http://thenonist.com/index.php/thenonist/permalink/stick_cha...

um_ya 7y ago

Imagine turning a wall into a mirror. Essentially, it uses a laser beam and fancy math to see around a corner, similar to looking at a mirror.

GistNoesis 7y ago

Imagine you have a cave the ceiling of which is covered by a thin film of water. At t=0, there is an explosion which shakes the water and make it fall vertically to the ground as droplets. You have a grid of water detectors on the grounds, which can tell you where and when a droplet hit the floor. If at t1 you detect a drop of water at floor coordinates (x,y), you know the height of the ceiling at (x,y) is h1 which you can compute from t1. So you can make an image of the ceiling. The paper algorithm is a fancier version of this, where the droplets are not falling straight down to the floor, but spread out like sphere ripples. So you need some fft math to deconvolve. The added benefit of using waves, is that you can see behind the objects, and you have a real 3D and not a 2.5D image.