Atmospheric Light Scattering (in low visibility)

[qhfreddy]

Hey guys, I'm kind of new around the forums and stuff so I am not exactly sure where to put this, so I just went with my best guess. (mods: Feel free to move if you deem necessary)

On to what I came here for:
I recently got back in to flight gear (Stopped a year or so ago with 1.92 on linux), started with 2.6, now running 2.10, and I was pleasantly surprised by some of the new graphical features.

But, after some MVFR flying with passenger jets I noticed a problem with the Atmospheric Light Scattering (ALS for simplicity's sake). The problem is that when running low visibility cover at dusk-dawn times (I only really fly around dusk and dawn, sometimes at night), most noticeably at dusk and dawn, the ground and other objects are visible in a dark outline at much further visibility than the intended visibility, or the visibility with the normal shader. Runway lights are visible through thick fog at 10km or more, buildings and the outlines of hills easily hundreds of kms. This kind of defeats the point of why I fly MVFR and (IFR conditions visually) in the first place, I can still see the runways and terrain as well, only the textures are less visible.'

Below is a screenshot at LOWI with the IFV IIIb preset, with the ALS on and under it one with it off, the difference is quite noticeable

[Thorsten]

See ongoing discussion on the devel list - the issue is recognized and you can expect some improvement in the future, but it's not a trivial problem.

The terrain outline is visible because the skydome unloads for visibilities below 1000 m, and so you get a mismatch between two rendering schemes. Lights stay visible for the same reason - they get the same fog color in the upper and lower pic, but since the terrain has a different fog color in the upper pic, it appears as if they remain visible despite them being 100% fogged. So lights need to be dispatched to a separate shader, the skydome needs to be kept, cloud fogging needs to be adjusted,... maybe we get it all done for 3.0.

Currently atmospheric light scattering works well for visibilities above 1000 m, but now much below, so if you really want to fly flow visibility, you're better off with the default scheme (which is also a computationally much cheaper option to render a fog-filled screen). Atmospheric Light Scattering does handle low light and high altitude much better than the default scheme though, so each scheme has its corners where it tends to fail.

[Lydiot]

the issue is recognized and you can expect some improvement in the future, but it's not a trivial problem.

I just wanted to see if there has been any development on this.

Yesterday it was foggy in NYC and while flying I noticed that the issue persists. In other words in low visibility with fog the runway lights are visible from great distances in most angles whereas without ALS it appears as I would think it should - i.e. lights become visible only in close proximity.

[Thorsten]

3.4 has a different bug with no runway lights in any rendering framework, but this is fixed now and will be okay in 3.6 - if you use point sprites, they fade properly in fog.

[Lydiot]

I'm confused. I have 3.4 and I see runway lights, so what do you mean by "no runway lights in any rendering framework"?

Also, are you saying that in order for it to work as I think we agree it should work (or look rather) I will eventually need 3.6 AND use point sprites?

Any clue when 3.6 will be out?

[wkitty42]

Any clue when 3.6 will be out?

[joke] after 3.5.0 has completed and been cooked long enough [/joke]

but seriously, 3.5.0 (the latest development version) has not reached the feature freeze point where only bugs are being worked on for the release...

FWIW: you might want to follow the development mailing list... you can read it via the mailing lists' archives link in the header and as well as signing up for the posts to be delivered to your email account for easier discussion responses and questions if you desire to write any

[Philosopher]

approximately 100 days.... seriously there is a nice release plan: http://wiki.flightgear.org/Release_plan, no need for "clues" or "guesses".

[Thorsten]

I'm confused. I have 3.4 and I see runway lights, so what do you mean by "no runway lights in any rendering framework"?

That...

Also, are you saying that in order for it to work as I think we agree it should work (or look rather) I will eventually need 3.6 AND use point sprites?

I think that's what I said, yes. We did write a consistent point sprite shader framework for the lights for 3.4 when the regression above was introduced and spoiled it on final, so the next chance is 3.6. And of course you need to use point sprites for the lights since we can only do shader effects for point sprites - the light dots are to my knowledge a fixed pipeline technique which can't be consistent with ALS.

[Lydiot]

k.

thanks.