A unified weather system?

[hvengel]

I don't care what the final answer is but I just want the ability to easily turn "off" weather.

I understand that's a rather strange statement as weather can never truly be "off", but I would like a generic, clear skies, variable visibility*, no winds at any level, throughout the entire earth, simply for ease of scenery testing and possibly for plane testing purposes.

Sorry that's not necessarily helpful to the discussion, but I feel it is important.

For those doing FDM work this would be a very handy feature. In fact I would like to be able to set things up for a totally windless standard conditions situation for FDM testing. This would allow for more accurate testing of things like rate of climb, speeds at various altitudes and so on. This does not even have to be in a menu as long as this mode could be reached using a command line switch or by setting some property.

[Hooray]

The local weather system already has the capability to disable the basic weather system, and it can also disable itself via the "clear/end" button - so it would not seem too difficult to provide a new switch or property to disable EVERYTHING.

[Johan G]

While I'm still running 2.4.0 I would guess that you could enter a windless METAR if you want zero winds and ISA conditions, though having a ready to use weather scenario with ISA conditions and no wind would of course be a better idea.

[KL-666]

Two of the questions in the initial message i would like to answer.

How important is METAR parsing vs. offline weather modelling for you?

As i fly a jetliner, going a couple of hundreds of miles from one to the next airport, i always use live metar. See the clouds change below me. Be surprised by the deteriorating weather at the arrival airport during descent.

On the other hand there are people fling in a small area wanting to create an interesting scenario i.e. GA pilots or fighter pilots.

So i think both possibilities should exist. I'd rather have them very separated, not necessarily engine-wise but control-wise i mean. I myself need nothing but what the live metar gives me. But some people might find the real weather to difficult to fly, so i can imagine just one slider for them: realistic to easy. Easy would cut off the sharp edges of the real weather. There is no need to bother them by a daunting set of settings. Make that separate and as complex as needed for the ones who want to create their own scenario.

Are there weather effects which are currently missing but should be modelled better?

There are 3 things that would really enhance the feel of realism for me.


1) Get a rough ride when the live weather is rough.

Currently wind variation (at airports where it is in live metar) seem to be only in the layer up to about 200 ft. I understand that metar information is limited and cannot be applied realistic to the higher air layers. On the other hand getting rough weather only in the last seconds of landing is also unrealistic. So i think making some educated guesses about what might be aloft is better than nothing. I have seen clouds at fl 300. That must also be an educated guess?

Maybe something like this can be done:

From a single metar, let the wind variation work higher, maybe up to a 1000 ft or even better 2000 ft, so a full final can be flown in rough winds.

If taking surrounding metars into account, one could lift the level of wind variation even higher, depending on how many surrounding metars also have wind variation in them.

If the latter is the case and the engine decides to draw cloud columns all the way to fl 300, then it might be plausible that the variable winds are also taken up to that height.


2) High altitude visibility

The standard visibility aloft seems to be fixed set on something like 25 mi. This makes you always fly in fog at fl 300. My experience in real flight is that often one can see much further at that altitude. Maybe here also an educated guess about aloft visibility can be made. Possibly based on pressure and humidity in the metar below.

For now i just raised the fixed visibility aloft a bit, so i do not fly in fog all the time. But that is also not realistic, to always have good visibility aloft.


3) Bigger 3D cloud field

With 3D cloud range at max (45 mi) and i fly at fl 300 and look down, i see a rather small football field of clouds below me at maybe fl 50. Not only does this look strange, but it also limits my options for aloft visibility settings. If i set visibility further than 45 mi i can look beyond the cloud field to ground which i should not see. So i limited the visibility aloft to 45 mi, which is still a quite short distance.

I am aware that 3D clouds eat gpu. So i was thinking, how to get more clouds with less gpu. Maybe there is a possibility to give them LOD ranges (or just couple them to current LOD). In that case you get nice clouds when flying in them. And coverage far away when flying high.


I hope some fg weather experts can use these thoughts (or have better ideas of their own) to forge a better live metar sky.

Kind regards, Vincent

[Thorsten]

All from Advanced Weather perspective:

Currently wind variation (at airports where it is in live metar) seem to be only in the layer up to about 200 ft. I understand that metar information is limited and cannot be applied realistic to the higher air layers. On the other hand getting rough weather only in the last seconds of landing is also unrealistic. So i think making some educated guesses about what might be aloft is better than nothing

That's intentional and I believe typically realistic.

Strong turbulence is in the model confined to the lowest convective layer (if caused by convection) or to the boundary layer (if caused by surface roughness - note that the boundary layer size is computed dependent on terrain roughness). I don't see the atmospheric physics justification to have turbulence and rough air reaching much higher - the only way they can be generated is thunderstorms (where we model it higher) and strong shear in airstreams with very different velocity (which are again a boundary phenomenon).

I don't think rough conditions extend very high aloft, and in my (limited) experience in reality that's also true - I've witnessed more than one landing where the bumpy ride started 4 minutes before touchdown.

The standard visibility aloft seems to be fixed set on something like 25 mi. This makes you always fly in fog at fl 300. My experience in real flight is that often one can see much further at that altitude. Maybe here also an educated guess about aloft visibility can be made.

That's already modelled and supported. Set LOD bare range to 120 km to get the terrain rendered, check 'realistic visibility' in the Advanced Weather options, set the max. visibility to 120 km, get 120 km visibility at cruise altitude (that's the limit because the far clipping plane in the renderer is set to 120 km - if you change that and recompile, I've also tested 250 km).

Bring a good graphics card and plenty of memory, you can fill several GB this way easily.

With 3D cloud range at max (45 mi) and i fly at fl 300 and look down, i see a rather small football field of clouds below me at maybe fl 50. Not only does this look strange, but it also limits my options for aloft visibility settings. If i set visibility further than 45 mi i can look beyond the cloud field to ground which i should not see. So i limited the visibility aloft to 45 mi, which is still a quite short distance.

That's a pure GUI limit - the engine supports 80 km draw range. The reason the GUI is set as it is is to avoid the never-ending stream of complaints about low performance. I regularly fly with clouds drawn to 80 km distance though.

Either edit the gui, or set the property using the property browser (it will remember the value for the next session) - it's /sim/rendering/cloud-visibility-range (or so) if I remember correctly. In the same directory there are also cloud LOD setting ranges (be aware that they currently mutilate faint clouds, so in order to get nice clouds, you need to render full-detail out to 75 km). Cloud LOD schemes are a science of its own, and about 100 times more complicated than you now think they are - I've been thinking about a good one for years, tested three or four, Stuart has implemented two so far, and still we aren't there.

Bring a high-end graphics card or watch your framerates drop into single digits.

[KL-666]

This advanced weather with live metar is a lot better than i could know from the dialogs. The only problem is that the settings and documentation are a bit hidden.

I extended my lod range and 3d cloud range, both to 80 mi, and cruise flight is suddenly beautiful if weather allows for it. Now i can fly over Caribbean islands and actually see them from fl 330. All this just at the cost of having 20 fps aloft, and a bit more up to 30 during landing. I think that is quite ok.

You are right about the 3 causes of turbulence. I was just speaking out of my flying experience where i had good turbulence for elongated periods at higher altitudes. In fg i did not experience them yet, but maybe i have never had the right conditions.

1) wind sheer: can last easily a quarter of an hour or longer (i guess when you fly quite parallel).
2) rising air: caused moderate turbulence in and below cumulus clouds (can be minutes) and very strong turbulence in storm clouds.
3) terrain effect: As you say, can surely be 4 minutes to landing.

If i make a little calculation with a final speed of 140 kts, then you get:

140 kts / 60 min * 4 min = 9.3 miles distance from runway. That is about start of glide slope from 2000 ft above the airport. I do not know if the calculation of wind variation in fg ever reaches 2000 ft. If it does not, maybe it can be taken into consideration to actually make it possible.

[Thorsten]

The only problem is that the settings and documentation are a bit hidden.

There are others for which they can't be hidden deeply enough Face it - the average user simply isn't interested in details of weather modelling...

In fg i did not experience them yet, but maybe i have never had the right conditions.

Look at this from a developer's perspective: METAR doesn't tell if there will be wind shear at high altitude. So in order to get it, you'd have to put it in more or less randomly. Assume I'd actually do this - then I'll get all the complaints 'The weather is broken - I suddenly got turbulence, but the METAR didn't say anything about it.'

Changing and gusty wind and turbulence are actually implemented a different way (the assumption being that turbulence has a stronger vertical component).

* Gusty winds are assumed to be the result of air friction on the terrain and hence always a boundary layer phenomenon. The boundary layer is computed dependent on the terrain roughness - over largely open water it is perhaps 100 ft high, in the mountains it can easily be 600-800 ft. The boundary layer also depends on altitude - in a mountain valley it may be 600 ft, but on mountaintops it is essentially zero (there's no wind slowdown).

* Turbulence is assumed to be the result of an unstable convective layer. You can influence convective layer stability with the thermal properties slider pushed towards 'rough day' (METAR doesn't really deliver the info). If you have strong winds and an unstable layer, you will get turbulence extending far above the boundary layer. At the same time, Cu clouds will visually appear more rugged. If you check 'generate thermals', thermals will be simulated underneath Cu clouds, including a region of turbulence surrounding them, and at 'rough day' conditions the thermals will be very narrow and strong.

* When a thunderstorm is created, the whole convective layer is assumed to be unstable and turbulence will occur all over the place regardless of the wind. Inside the Cb tower, there will be extremely strong turbulence, strong updraft and heavy precipitation.

It'd be technically easy to create turbulence at high altitude, simulating wind shear. The problem is determining the conditions under which this would occur, as I think it would have to be consistent with the aloft wind modelling, but we don't really have that to such high resolution as to be able to look for strong gradients. Maybe I put some of this into the offline weather system (that has a much better idea about what the weather is like, since it doesn't have to rely on ground observation only but 'knows' what goes on in the upper atmosphere). You might want to give it a try at some point as well - it's quite as capable of delivering changing weather, and in addition it comes with weather fronts (which are impossible to do properly from METAR) and a good model for visibility gradients in the upper atmosphere.

[KL-666]

Today i got convinced the current advanced weather model makes the live wind variation interesting enough. Near Las Vegas - Amarillo i got shaken up good at more than 10000 ft above the ground. Must have been the convection type. Now i am air-sick. I love it!

The only thing that worries me now are the 3D clouds. They do eat a lot of gpu. I know i set distance to 80 mi, but often i see almost no clouds. Either they are eaten by sky blend or i am so low that i can never see 80 mi. Maybe in those circumstances the 3d cloud distance can be temporarily reduced to a distance that they are realistically visible. Then in many cases frame rates would be better than in the worst case (80+ mi visibility at altitude).

[Thorsten]

Maybe in those circumstances the 3d cloud distance can be temporarily reduced to a distance that they are realistically visible.

The system doesn't build clouds over terrain beyond visibility range because it can't - in order to get the interaction between clouds and terrain right, you need to have terrain loaded into memory. So if you're low and have 30 km visibility, you won't generate clouds out to 80 km. Btw. - the cloud visibility control is still technically a slider (even if you edited the property) - so you can adjust it whenever your framerate drops.

But ultimately, as I said - bring a good GPU... There is no cheap scheme for rendering halfway realistic 3d clouds I would know of.

[KL-666]

Hi Thorsten,

I hope you read this thread still. Today i found out an amazing framerate-boost. If i turn on 3d-clouds at the startup widget, i get horrible framerates with many clouds, like below 5 fps. But if i do not check 3d-clouds at startup, but enable it from the menu/view options, then i get relatively great fps with the same clouds, like 15-20 fps. I thought you should know, Thorsten, so you may tell the difference technically and maybe equal them, for the good frame-rates ofcourse.

Kind regards, Vincent

[KL-666]

Ok, now i got the really very best setting for advanced weather and 3d-clouds. Turn off 3d-clouds completely. They are already delivered by advanced weather. I did not realize that before, so i had "double" 3d-clouds, which had quite an impact on fps.

Hope this helps anyone with advanced weather and low frame rates.

Kind regards, Vincent

[Thorsten]

There's something odd here - there shouldn't be anything double. Can you describe exactly what you do so that I can follow this up? Do you alter cloud density and / or LOD ranges in any way implicitly? Can you check cloud-related entries in /sim/rendering in the property tree?

[KL-666]

Hi Thorsten,

I am quite happy with the situation as is, with 3d-clouds off, as they are still coming from advanced weather. Makes a diff of about 20 fps, especially below the clouds, which is good for landing. But fyi the setings of 3d-clouds:

density = 1
detail-range = 3000
enable = false
impostor-range = 15000
lod1-range = 2000
lod2-range = 1000
use-impostors = false
vis-range = 80000
wrap = false

Kind regards, Vincent

[Thorsten]

I can't reproduce this - I've written a message to the devel list to see if anyone else can. If we can really gain 20 fps somewhere, that'd be important, but I can't see where this may originate from.

[KL-666]

Hi Thorsten,

The fps gain differs per situation, but there is always gain.

With no or few clouds:
- 3d clouds on: max 20 fps
- 3d clouds off: way over 30 fps

With many clouds:
- 3d clouds on: less than 5 fps
- 3d clouds off: around 10 fps

With many clouds getting below the clouds the fps goes up to 15-20. This does not happen when 3d clouds are on.

Another thing i wanted to ask you is:

There is a big difference in impact depending on type of clouds. The worst are the type that look like an overcast of packed cumulae (i call them horrible clouds). I think the reason these clouds have such an impact is that every individual cloud is calculated very precise. If this is the case, could there not be a bit less calculation, since these clouds are actually one big pack?

And yet another thing:

Sometimes after a couple of hours flying, the fps may gradually deteriorate and do not get better anymore with flying into other metars (10 fps or less). After landing i then reload the weather by opening the weather dialog and hit ok. Suddenly the fps jumps up to 20-30 fps or even more (depending on type of clouds) and stays so for a long time again.

As i reloaded the same metar that i had on landing, i suspect the cloud system leaks somewhere. Maybe it keeps doing things for the metars i passed during flying, which are far away now?

Kind regards, Vincent