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No shadows in FSX or FG 3.0 what's with these modern sims?

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Re: No shadows in FSX or FG 3.0 what's with these modern sim

Postby erik » Mon Oct 19, 2015 9:33 pm

http://www-spof.gsfc.nasa.gov/stargaze/StarFAQ2.htm#q37
The Sun covers about half a degree of the sky. So rays that come from opposite edges of the Sun have directions which differ by half a degree and are not parallel.


Not as much as you would expect given the size of the sun.
One way to explain this is that your eye is a lens which casts the near parallel rays onto your retina.

That said, half a degree will be noticeable, but much less that scattering from pollution or haze.

Update: A quick calculation shows that a B747 will cover half a degree at 5000ft, which means at least up to that altitude it will cast a noticeable shadow.

Erik

Thinking about this I do however wonder how the wavelike behavior of photons make a difference.
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Re: No shadows in FSX or FG 3.0 what's with these modern sim

Postby Thorsten » Tue Oct 20, 2015 5:49 am

Not as much as you would expect given the size of the sun.


Sorry, you lost me. I expected half a degree based on the angular size of the sun in the sky earlier in this thread. The size of the sun over the distance to earth happens to work out to an angle of half a degree - that's all there is to it.

A quick calculation shows that a B747 will cover half a degree at 5000ft, which means at least up to that altitude it will cast a noticeable shadow.


No, it means that if only ray optics is relevant, there is a (gradually shrinking) shadow generated which vanishes at 5000 ft. It's an upper limit, because both wave diffraction and scattering on air will further decrease your shaded region. Also, the 747 is not a disc, and having only a small patch of sun uncovered is enough to remove a shadow.

In actual reality, the shadow will be gone somewhat before that altitude, though it's hard to say for sure when exactly.

Note that a good part of the effect of haze and air scattering is however accounted for by counting direct (diffuse and specular) and indirect (ambient) light - the depth of a shadow depends on the strength of ambient light over diffuse light, which in turn depends on haze (often that is Rayleigh light, which is why shadows are somewhat blue on a clear day). So there's only a specific scattering channel (mostly Mie scattering of rays just missing the airplane into the shadow cone) which tends to remove the shadow specifically as a function of distance.
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Re: No shadows in FSX or FG 3.0 what's with these modern sim

Postby erik » Tue Oct 20, 2015 7:29 am

Now you're just trying to win an argument.
Fine. discussion closed.
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Re: No shadows in FSX or FG 3.0 what's with these modern sim

Postby Thorsten » Tue Oct 20, 2015 8:14 am

Look, I happen to be a theoretical physicist. I can compute light propagation on the quantum level if needed, and I think I do understand ray and wave optics quite well. I know what the shadow does with distance, and if given time, I can even write a code that exactly tells you when and how it goes away as a function of air and aerosol density - the equations aren't that difficult, I just can't do them in my head.

All I'm trying to do is tell you where your intuition leads you astray and what effects come into play in reality. If you're not interested, that's fine with me. I don't need to win the argument - nature does that for me.
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Re: No shadows in FSX or FG 3.0 what's with these modern sim

Postby erik » Tue Oct 20, 2015 9:21 am

We were basically saying the same, there was no need to continue arguing if you'd ask me.

Erik
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Re: No shadows in FSX or FG 3.0 what's with these modern sim

Postby Thorsten » Tue Oct 20, 2015 10:14 am

For whatever it's worth, I just did some quick estimates:

* diffraction is negligible in reducing shadows as compared to other effects

* Mie scattering, if strong between object and eye, can potentially cause the shadow cone to shrink with an angle of 1 deg instead of half a deg, i.e. can reduce the range the shadow shows by half

Fun fact - for many relevant key word combinations ('mie scattering sky', 'mie scattering sun', 'mie scattering cloud') google actually finds FG screenshots on the first page.
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Re: No shadows in FSX or FG 3.0 what's with these modern sim

Postby erik » Tue Oct 20, 2015 10:31 am

:)
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Re: No shadows in FSX or FG 3.0 what's with these modern sim

Postby Johan G » Wed Oct 21, 2015 10:44 am

Thorsten wrote in Tue Oct 20, 2015 10:14 am:Fun fact - for many relevant key word combinations ('mie scattering sky', 'mie scattering sun', 'mie scattering cloud') google actually finds FG screenshots on the first page.

That is due to your work (and us taking screenshots). :D
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Re: No shadows in FSX or FG 3.0 what's with these modern sim

Postby Johan G » Thu Oct 22, 2015 4:55 am

Some posts were split off to the new topic Avoiding contributing to SEO for the Flight Pro Sim scam.
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Re: No shadows in FSX or FG 3.0 what's with these modern sim

Postby openflight » Thu Oct 22, 2015 6:48 am

This is all a little beyond me - but put simply, having the aircraft shadow turn off at take -off will cover 90% of the scenarios that would be ecountered in real life?
We are talking about aicraft-ground shadows.

Aircraft-same aircraft shadows are another matter- best to look at actual photos of aircraft in flight. Or aircraft landing and taking off.

A little search shows me this: see the third photo - a real aircraft, no shadows :shock: Why is reality so complicated ?

http://www.cessna150-152.com/aotm/coverplane200505.htm

This one has - bright sunlight?

http://www.airport-data.com/aircraft/ph ... 05082.html

This one as well

http://www.airport-data.com/aircraft/ph ... 9764L.html
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Re: No shadows in FSX or FG 3.0 what's with these modern sim

Postby Johan G » Thu Oct 22, 2015 7:16 am

openflight wrote in Thu Oct 22, 2015 6:48 am:A little search shows me this: see the third photo - a real aircraft, no shadows :shock: Why is reality so complicated ?

http://www.cessna150-152.com/aotm/coverplane200505.htm

Oh, it is there. It is just very diffuse, probably due to (thin) overcast clouds.
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