3 ms·

It would be cool if it could factor in mountains - but I get why that is not an easy task. Fun isn't the best word to describe this page - but it was!

jvanderbot 4y ago
It's conceptually simple : use visibility based on viewshed for heat and direct blast concussion. Secondary effects (wind) would be harder. But it's computationally extremely difficult, as you say.
- TeMPOraL 4y ago
  Well, you could cheat. There's so much cheap GPU compute used for mining shitcoins and training glorified Markov chains on Reddit dumps, surely someone could spare a few racks to run some CFD on a detailed GIS model of our planet, to create lookup tables that would allow everyone to cheaply simulate all kinds of fun events, such as nuclear detonations, asteroid impacts, "rods of god", relativistic kill vehicles, supervolcano eruptions, etc. anywhere on the planet, at the push of a button. The social value of this would be immense - even if you and me never used those precomputed LUTs for anything, they would surely help Randall Munroe or Kurzgesagt or others answer even more high-energy "what-if" questions with even greater accuracy!
  - vba616 4y ago
    >surely someone could spare a few racks to run some CFD on a detailed GIS model of our planet, to create lookup tables that would allow everyone to cheaply simulate all kinds of fun events, such as nuclear detonations, asteroid impacts, "rods of god", relativistic kill vehicles, supervolcano eruptions, etc. anywhere on the planet, at the push of a button. Nobody ever did a sequel to https://en.wikipedia.org/wiki/SimEarth https://en.wikipedia.org/wiki/SimEarth ?
    - mehwoot 4y ago
      shameless plug: https://store.steampowered.com/app/1482770/Terra_Firma/ https://store.steampowered.com/app/1482770/Terra_Firma/
  - j5155 4y ago
    I would love to mess with that, but I think it also be used for targeting weapons with even greater accuracy, not just theoretical questions
    - throwaway290 4y ago
      Security through obscurity?
  - throwaway290 4y ago
    A depressing picture that I agree with yet the way you left not a single thing unburned made me laugh. (Thanks, I needed it)
- btschaegg 4y ago
  I don't think visibility would be all that hard to compute for the purposes of this site; I did similar calculations for radio "visibility" once (four thirds earth radius etc.): - Choose a grid of square cells of appropriate size (can be quite large here) - Put it on a plane tangential to an idealized flat earth ground at the center (easy in ECEF) - Offset by the desired height - Perform a "raycast" from the center cell to the center of each other cell - Calculate elevation from interpolated SRTM data along the way and store the maximum elevation* along the path (idea: something similar to DDA traversal through the SRTM data? Wouldn't be exactly linear, though…) - You can pretty much derive anything via linear algebra from there * "Elevation" from the viewpoint of the chosen plane, obviously.
  - jvanderbot 4y ago
    Visibility is not hard to compute. I said you could use "viewshed", which is the usual method of calculating line of sight to a given point from all points in an area. But it is a computationally intensive task to take a large enough area to accommodate any arbitrary asteroid impact. Orders of magnitude more than a web response, even accounting for down sampling and heuristics to restrict the size of the compute area. Almost any GIS software package can do it for you. https://en.m.wikipedia.org/wiki/Viewshed https://en.m.wikipedia.org/wiki/Viewshed What you're suggesting is that, except you didn't account for curvature of earth.
    - btschaegg 4y ago
      > Orders of magnitude more than a web response That's likely where our different assesments come from, then. I was thinking more along the lines of "it's parallalelizable and easily offloaded to the client". An addendum for completeness' sake, though :) > What you're suggesting is that Not entirely. I'd build a LUT of "how high up must you be to be visible here" per "pixel", instead of "is the ground here visible", which I'd argue is more useful for modelling here. > except you didn't account for curvature of earth I didn't spell it out explicitly, but that's not the case if you do your projections right. (And you have to project, as SRTM data is always relative to the EGM96 geoid.)

jvanderbot 4y ago

It's conceptually simple : use visibility based on viewshed for heat and direct blast concussion. Secondary effects (wind) would be harder. But it's computationally extremely difficult, as you say.

TeMPOraL 4y ago
Well, you could cheat. There's so much cheap GPU compute used for mining shitcoins and training glorified Markov chains on Reddit dumps, surely someone could spare a few racks to run some CFD on a detailed GIS model of our planet, to create lookup tables that would allow everyone to cheaply simulate all kinds of fun events, such as nuclear detonations, asteroid impacts, "rods of god", relativistic kill vehicles, supervolcano eruptions, etc. anywhere on the planet, at the push of a button. The social value of this would be immense - even if you and me never used those precomputed LUTs for anything, they would surely help Randall Munroe or Kurzgesagt or others answer even more high-energy "what-if" questions with even greater accuracy!
- vba616 4y ago
  >surely someone could spare a few racks to run some CFD on a detailed GIS model of our planet, to create lookup tables that would allow everyone to cheaply simulate all kinds of fun events, such as nuclear detonations, asteroid impacts, "rods of god", relativistic kill vehicles, supervolcano eruptions, etc. anywhere on the planet, at the push of a button. Nobody ever did a sequel to https://en.wikipedia.org/wiki/SimEarth https://en.wikipedia.org/wiki/SimEarth ?
  - mehwoot 4y ago
    shameless plug: https://store.steampowered.com/app/1482770/Terra_Firma/ https://store.steampowered.com/app/1482770/Terra_Firma/
- j5155 4y ago
  I would love to mess with that, but I think it also be used for targeting weapons with even greater accuracy, not just theoretical questions
  - throwaway290 4y ago
    Security through obscurity?
- throwaway290 4y ago
  A depressing picture that I agree with yet the way you left not a single thing unburned made me laugh. (Thanks, I needed it)
btschaegg 4y ago
I don't think visibility would be all that hard to compute for the purposes of this site; I did similar calculations for radio "visibility" once (four thirds earth radius etc.): - Choose a grid of square cells of appropriate size (can be quite large here) - Put it on a plane tangential to an idealized flat earth ground at the center (easy in ECEF) - Offset by the desired height - Perform a "raycast" from the center cell to the center of each other cell - Calculate elevation from interpolated SRTM data along the way and store the maximum elevation* along the path (idea: something similar to DDA traversal through the SRTM data? Wouldn't be exactly linear, though…) - You can pretty much derive anything via linear algebra from there * "Elevation" from the viewpoint of the chosen plane, obviously.
- jvanderbot 4y ago
  Visibility is not hard to compute. I said you could use "viewshed", which is the usual method of calculating line of sight to a given point from all points in an area. But it is a computationally intensive task to take a large enough area to accommodate any arbitrary asteroid impact. Orders of magnitude more than a web response, even accounting for down sampling and heuristics to restrict the size of the compute area. Almost any GIS software package can do it for you. https://en.m.wikipedia.org/wiki/Viewshed https://en.m.wikipedia.org/wiki/Viewshed What you're suggesting is that, except you didn't account for curvature of earth.
  - btschaegg 4y ago
    > Orders of magnitude more than a web response That's likely where our different assesments come from, then. I was thinking more along the lines of "it's parallalelizable and easily offloaded to the client". An addendum for completeness' sake, though :) > What you're suggesting is that Not entirely. I'd build a LUT of "how high up must you be to be visible here" per "pixel", instead of "is the ground here visible", which I'd argue is more useful for modelling here. > except you didn't account for curvature of earth I didn't spell it out explicitly, but that's not the case if you do your projections right. (And you have to project, as SRTM data is always relative to the EGM96 geoid.)