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Old 06-07-2011, 02:22 AM   #16
PeterRoss
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Originally Posted by Donamy View Post
 could this involve moving cloud patterns ?
Having some connection between wind and clouds will let us have real sandstorms on Mars!
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Old 06-07-2011, 02:59 AM   #17
martins
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 could this involve moving cloud patterns ?
Dynamic cloud patterns on a global scale is a big ask. Maybe we could start with some more modest applications, like the occasional tumbleweed ball rolling through the picture ...

Edit:

Seriously though, the wind vector field could be used as a displacement field for distorting the cloud texture map. This is something similar to nonrigid registration frequently used in medical imaging. The difference is that for registration, this is a single, linear operation, or at least a modestly nonlinear operation over a finite range. For clouds this would be a completely nonlinear problem over an infinite range. I.e. you take the vector field to displace the clouds from one time frame to the next, then use the same displacement field on the new texture for the next time frame, etc. This may work over very small time frames (a few hours, unless there are extreme wind speeds involved) but beyond that, the cloud patterns will quickly become invalid.

In addition, coulds don't just move. They also form and disperse, so other factors like temperature, pressure, vertical velocity components, moisture, evaporation and condenstation, etc. will have to be taken into account. This quickly leads to an atmospheric model that is magnitudes more complicated than orbiter itself.

A proper model-based solution like this is beyond the scope of orbiter, but some more hacky approaches could be more feasible (like using multiple cloud maps taken at intervals of some hours, and slowly blending from one to the next. Except for the jump when you cycle back to the first image in the sequence, this may not look too bad).
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Old 06-07-2011, 04:43 AM   #18
PeterRoss
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Originally Posted by martins View Post
 Dynamic cloud patterns on a global scale is a big ask. Maybe we could start with some more modest applications, like the occasional tumbleweed ball rolling through the picture ...
Well, they say one guy said something about asking something for it to be given Seriously, you'll have to make your windmap discrete anyway, so why not to combine it with cell texturing of cloud layers? (Now they'll tell me I'm speaking some nonsense here... Oh, can a man dream?)
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Old 06-07-2011, 04:45 AM   #19
Krikkit
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Edward Lorenz was trying to model global atmospheric patterns when he discovered chaos theory. So needless to say this will be no trivial matter and I wish you the best of luck.
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Old 06-07-2011, 08:55 AM   #20
Ripley
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Originally Posted by N_Molson View Post
 ...The axial tilt was a very important factor, with the difference of temperature between the day and night sides...
And land <--> sea mass, too.
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Old 06-07-2011, 11:28 AM   #21
Wishbone
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Other than for remote sensing and Cumulonimbus avoidance, clouds serve no useful purpose for spacefarers. Unless someone plans to dogfight in the atmosphere, this feature is IMHO not worth the expenditure of time to code and debug. You could add optical depth as another moddable and pluggable callback function, though:

Code:
double clbkOpticalDepth(const OBJHANDLE hBody, 
                                 const double Lon, 
                                 const double Lat,
                                 const double MJD) const;
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Old 06-07-2011, 11:30 AM   #22
RisingFury
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Finally! This is gonna make reentries awesome again!

I do have a question... how will this work with existing addons? Mainly I want to know what happens to functions that return airspeed. Will you change them to include wind speed as well? Will you add a GetAirspeedEx with a parameter to include wind or to exclude it?
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Old 06-07-2011, 11:56 AM   #23
Spacethingy
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Oooooooooo! Wind! Excellent. Thanks Martin! That'll add a nice extra level of detail, having to deal with weather!

Finally, the wind sound in OrbiterSound will actually mean something...

Edit: and this will have use too...
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Old 06-07-2011, 12:35 PM   #24
Moach
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with weather and procedural terrain, Orbiter could very well take on M$FS one of these days... and it would win, dead sure

we need more runways
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Old 06-07-2011, 12:39 PM   #25
martins
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Originally Posted by RisingFury View Post
 Finally! This is gonna make reentries awesome again!

I do have a question... how will this work with existing addons? Mainly I want to know what happens to functions that return airspeed. Will you change them to include wind speed as well? Will you add a GetAirspeedEx with a parameter to include wind or to exclude it?
No, the GetAirspeed function will automatically include wind speed. Instead there will be a new function GetGroundspeed which will exclude the wind speed. This seems a more consistent convention than having a function called GetAirspeed to return ground speed, and GetAirspeedEx to return the actual airspeed. I don't see that as a problem with backward compatibility. Until now, GetAirspeed returned the correct airspeed value, because wind speeds were zero. I am simply extending this by introducing nonzero wind speeds.

The only problem is that addons that actually meant "ground speed" when calling GetWindspeed will have to be modified. But this doesn't seem to be worse than forcing modifications to the addons which really meant "airspeed".
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Old 06-07-2011, 03:29 PM   #26
jangofett287
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Naturally there will be a launchpad tick-box to enable/disable the wind I assume? This would sort out backwards compatibility and low end computers.
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Old 06-07-2011, 03:38 PM   #27
Ripley
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Quote:
Originally Posted by martins View Post
 ...What do other flight simulators use?
X-Plane downloads real METAR data.
http://code.google.com/p/fjccunivers...c=svn245&r=245

Last edited by Ripley; 06-07-2011 at 04:17 PM.
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Old 06-07-2011, 03:48 PM   #28
ky
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We might as well add weather like rain or thunderstorms into this.If we do we could easily take on MSFS or MF(microsoft flight)as it's called now.Also take a look at this:http://cboard.cprogramming.com/cplus...ind-speed.htmlI hope its of some help.
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Old 06-07-2011, 04:05 PM   #29
martins
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 Also take a look at this:http://cboard.cprogramming.com/cplus...ind-speed.htmlI hope its of some help.
Wind speed perturbations drawn from a uniform distribution with hard edges, and an arbitrary correlation length of 10 seconds, determined by the sample density? I sincerely hope that this is not how flight simulator models its wind speed! If the guys in that thread had at least used a normal distribution, it wouldn't look so bad ...

No, I think for orbiter we should be able to come up with something a bit more sophisticated.
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Old 06-07-2011, 04:12 PM   #30
Ripley
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Quote:
Originally Posted by martins View Post
 ...What do other flight simulators use?
FlightGear also uses METAR plus Jeppesen data

http://wiki.flightgear.org/Howto:_Fetch_live_aloft_data
http://www.jeppesen.com/aviation/per...on-weather.jsp


Condor: The Competition Soaring Simulator features (but this is maybe beyond our scope)
Realistic thermals life cycle: starting from the ground they reach cloud base, the cloud becomes bigger and more dense and later dissipates which causes the air below it to sink.
The location and strength of thermals is based on terrain sun exposure and ground features like forests, fields and villages.
Realistic daily sun travel which affects the frequency and strength of thermals.
Up slope wind on sunny ridges (anabatic winds).
Ridge lift with leeward downwind and turbulence, venturi effects.
Waves behind ridges, wavelength depends on wind speed and stability of the atmosphere.
Correct atmosphere pressure, density and temperature height distribution.
3D isotropic turbulence model for thermal and mechanical turbulence.
preset and custom weather conditions.

Last edited by Ripley; 06-07-2011 at 04:16 PM. Reason: Added Condor
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