FlightGear wiki - User contributions [en]

Commonly used debugging tools

2015-08-05T11:15:36Z

Tigert: /* Command line */ comment that the log level names wont work in capital case.

{{stub}}

There are some relatively simple but '''commonly used debugging tools''' that might answer questions of for example why your installation of FlightGear will not run properly or at all, why an aircraft might have problems or why flying in a certain area always cause FlightGear crashes.

The more useful of those tool are the console window (also known as the "black box" or confusingly the "command line"), the <code>fgfs.log</code> file and the property browser.

There are of course times when these will not do, and sometimes one would have to compile FlightGear from source ''and'' add some additional debugging features to find some bugs.

== Debug level setting ==
Before we go any further we should mention the ''debug level'' setting (also known as ''log level''). When FlightGear runs it will output information on various things. As a default only things that are expected to cause troubles are output, but by setting a higher debug level more information will be shown. At the highest debug level one can expect FlightGear to run slow due to all the debug output.

=== Debug levels ===
There are five debug levels:
; Bulk: Will output very frequent messages. Using this setting might slow down FlightGear a lot, but might show problems not otherwise found.
; Debug: Will output less frequent debug messages.
; Info: Will output informatory messages.
; Warn: Will output messages about possibly impeding problems.
; Alert: Will output messages about very possibly impeding problems. This is the default level.

=== Setting the debug level ===
==== FGRun ====
In FGRun go to the last page click {{key press|Advanced...}} then, in the list to the left, click "Debug" and then chose the desired debug level in the list.

==== Command line ====
Add <code>--log-level=''debug level''</code> to your command line. The names need to be in lowercase: <code>debug</code>, not Debug.

== The console window ==
Before FlightGear 2.6 this was always opened in a separate window when starting FlightGear through the [[FGRun]] wizard, but these days it is normally hidden and can be shown by ticking a checkbox, "Show command line".

== fgfs.log ==
The startup log file contains nearly the same information that is output on the console.

=== Finding fgfs.log ===
; Mac: <code>~/Library/Application Support/FlightGear/fgfs.log</code>
; Windows: <code>C:\Users\''user name''\AppData\Roaming\flightgear.org\fgfs.log</code>
; Linux: <code>~/.fgfs/</code>

== The property browser ==
{{main article|Property browser}}
The property browser is a tool useful for many purposes. It might for example tell if a property is tied and can not be written to.

== Related content ==
* [[Command line]]
* [[Property browser]]
* [[Howto:Understand console output]]
* [[:Category:Troubleshooting]]

== External links ==
* [https://gitorious.org:443/fg/simgear/source/deceee899771b82b0568319863b3812b272c926d:simgear/debug/debug_types.h#L44 The debug levels as mentioned in the source code]

[[Category:Troubleshooting]]
[[Category:Aircraft enhancement]]

Project Farmin

2015-06-23T12:46:07Z

Tigert: /* Screen Shots */

{{infobox subsystem
|image =FARMINLogo.png
|started= 01/2015
|description = [[Canvas]] and [[MapStructure]] based Flight deck Framework (see: [[Canvas Animation Framework]]/[[Canvas MFD Framework]])
|status = Early Prototyping for the FG1000 PFD
|maintainers = www2
|developers = www2
|topic-fgdata= {{Git link|gitorious|fg/farmin-fgdata|master:Aircraft/Instruments-3d/Farmin }}
|folders = $FG_ROOT/Aircraft/Instruments-3d/Farmin
}}

'''Project Farmin''' is a project aiming at making an aircraft independent framework simulating the Garmin flight decks (G500(H), G600, G900X, G950, G1000(H), G2000, G3000, G5000(H)).

Currently the focus is on the G1000 that is in use on 1 or 2 engine props and jets, for example Cessna 172R/S, 208/208B Caravan, Mustang and Embraer Phenom.

== Background ==
{{FGCquote
|Canvas itself is a great piece of technology, but using it to implement complex MFDs is like asking someone to create an object-oriented and multi-threaded application using assembly language: it is possible, but very tedious and requires tons of experience and expertise. This is basically the reason why the most generic Nasal/Canvas code was typically written by people already familiar with FG/SG and OSG internals (i.e. core developers).
|{{cite web |url=http://forum.flightgear.org/viewtopic.php?p=231068#p231068
|title=<nowiki>Re: Project </nowiki>
|author=<nowiki>Hooray</nowiki>
|date=<nowiki>Mon Feb 02</nowiki>
}}
}}

{{FGCquote
|Canvas is an important piece of technology in FlightGear, but it really is just a "toolbox" providing low-level tools for 2D drawing via OpenVG primitives, raster/vector images, and osgText. 
However, you'll find that when designing complex MFDs, you need much higher-level functionality, ideally encapsulating important shared concepts - such as having components ({{=}}classes) for things like: 
 
<ul>
<li> MFD class</li>
<li> Screen class</li>
<li> Page class</li>
<li> PageManager class</li>
<li> Layout/LayoutManager class</li>
<li> Button/switch class</li>
<li> Mode class</li>
<li> Animation class</li>
</ul>

|{{cite web |url=http://forum.flightgear.org/viewtopic.php?p=231068#p231068
|title=<nowiki>Re: Project </nowiki>
|author=<nowiki>Hooray</nowiki>
|date=<nowiki>Mon Feb 02</nowiki>
}}
}}
{{FGCquote
| this is more about identifying requirements first and coming up with a few simple framework for your requirements - which normally also means that others working on unrelated instruments would benefit from those changes, and might even team up at some point (which is what happened to the ND effort, we've seen people contribute to Gijs' 744 ND code, despite never having taken any interest in the 744 at all, simply because that code now allows "styles" to be configured for other airliners)
|{{cite web |url=http://forum.flightgear.org/viewtopic.php?p=231068#p231068
|title=<nowiki>Re: Project </nowiki>
|author=<nowiki>Hooray</nowiki>
|date=<nowiki>Mon Feb 02</nowiki>
}}
}}

{{FGCquote
|Canvas is still a relatively new feature in FG terms, and like I said, it being pretty low-level, it is conceivable that Canvas will continue to be extended over time to provide better building blocks, or even just better performance - however, doing so is only feasible if people adopt a framework-centric development approach, so that key functionality is properly "encapsulated" (e.g. through a helper class) - which means that if/when more native ({{=}}faster) Canvas animation support should be added, we would only need to update the single helper class encapsulating the concept of an '''Animation''' - however, what is currently being done all over the place in fgdata, is that Nasal/Canvas related code is written from scratch without things being encapsulated at all - in other words, even if Tom should make a huge commit tomorrow improving Canvas performance/efficiency by 500%, we would still need to manually port/update all the legacy code, because there's no encapsulation taking place. 
 
 
Overall, we want to support complex MFDs via Canvas, but people should really share their work much earlier so that we can come up with a subset of common/overlapping goals and find a way to meet all requirements, without adding even more problematic Nasal code to the FlightGear base package.
|{{cite web |url=http://forum.flightgear.org/viewtopic.php?p=231068#p231068
|title=<nowiki>Re: Project </nowiki>
|author=<nowiki>Hooray</nowiki>
|date=<nowiki>Mon Feb 02</nowiki>
}}
}}

== Development ==

{| class="wikitable"
|-
! Status !! Farmin !! Garmin !! Family !! Manual on Garmin site* !! Extra info
|-
| {{progressbar|10}} || [[Project_Farmin/FG500|FG500]] || G500 || G500/G600 || True || None
|-
| {{progressbar|10}} || [[Project_Farmin/FG500|FG500H]] || G500H || G500/G600 || True || Helicopter version of the FG500/G500
|-
| {{progressbar|10}} || [[Project_Farmin/FG500|FG600]] || G600 || G500/G600 || True || None
|-
| {{progressbar|10}} || [[Project_Farmin/FG1000|FG900X]] || G900X || G1000 || False || Flight deck for kitplane
|-
| {{progressbar|10}} || [[Project_Farmin/FG1000|FG950]] || G950 || G1000 || True || OEM/after market
|-
| {{progressbar|10}} || [[Project_Farmin/FG1000|FG1000]] || G1000 || G1000 || True || None
|-
| {{progressbar|10}} || [[Project_Farmin/FG1000|FG1000H]] || G1000H || G1000 || True || Helicopter version of the G1000
|-
| {{progressbar|10}} || [[Project_Farmin/FG3000|FG2000]] || G2000 || G3000 || True || 2 Screens and 1 touchscreen
|-
| {{progressbar|10}} || [[Project_Farmin/FG3000|FG3000]] || G3000 || G3000 || True || 3 Screens and 2 touchscreen
|-
| {{progressbar|10}} || [[Project_Farmin/FG3000|FG5000]] || G5000 || G5000 || False || Up to 4 screens and 4 touchscreen
|}
* This mean not that the manuals are on the web

== Components ==
=== MFD ===
Top level helper class managing all related components.

=== ImageSource ===
An ImageSource will be an invisible Canvas representing the video/graphics output of a display.
<syntaxhighlight lang="nasal">

var ImageSource = {
new: func(x,y) {

var m = {parents:[ImageSource]};
m.canvas = canvas.new({
"name": "ImageSource-"~name,
"size": [x, y],
"view": [x, y],
"mipmapping": 1

});
return m;
},
del: func() {
},
};
</syntaxhighlight>

=== Screen ===
A Screen will merely be a placeholder for another Canvas referenced via canvas:// - so that arbitrary placements can be used to display a MFD screen.
<syntaxhighlight lang="nasal">
var Screen = {
new: func() {
},
attach: func(source) {
},
del: func() {
},
};
</syntaxhighlight>

=== ImageSourceSelector ===
A helper class to manage multiple image sources and hook them up to screens - i.e. for allowing MFDs to be shown on different screens.
<syntaxhighlight lang="nasal">
</syntaxhighlight>

== Screen Shots ==

Some screen shots are posted on the forum thread (see below)

== Related content ==
=== Forum topic ===
* [http://forum.flightgear.org/viewtopic.php?f=14&t=25291 Project Farmin <nowiki>[</nowiki>Garmin Flightdeck Frame work<nowiki>]</nowiki>] – ''Development topic on the forum''

[[Category:Project Farmin]]

Realism

2015-03-13T07:24:37Z

Tigert: /* Weather */

{{cleanup}}

How realistic is [[FlightGear]]'s [[aircraft]] and environment? What is needed to get more realism and immersion from the FlightGear environment?

== Aircraft ==

[[File:DR400_Dauphin_Rembrandt_02.jpg|800px|center|The [[DR400|DR400 Dauphin]].]]

The underlying instrumentation models are very accurate, with many physical effects accounted for.

* The heading indicator has a small delay when it's slewing to your heading.
* The artificial horizon can tumble.
* The magnetic compass will rotate in all three axes and get stuck if the aircraft is tilted.
* The altimeter uses air pressure to determine altitude; if the sea level air pressure is set incorrectly, it will display the wrong altitude as in real life.
* All of the instruments that need engine power in real life are tied to the virtual engine; if the engine is not running, all vacuum-powered instruments (such as the artificial horizon and the heading indicator) will not function properly.
* Some aircraft feature accurate electrical systems with batteries that will drain over time and instruments that need electricity.

== Flight dynamics ==

Since FlightGear uses many [[FDM|flight dynamics models]] under the hood, including [[YASim]] and [[JSBSim]], the realism of an aircraft depends on its FDM. Both of these support winds and turbulence; YASim generally has more realistic ground interactions with different surfaces, while JSBSim FDMs are generally truer to the real-life aircraft. It's important to note that both of these can produce similar results if the FDM is worked on enough.

== Scenery==

<gallery mode="packed">
File:Southwest04.jpg|
File:Kansas_Scenery_Two.jpg|
</gallery>

* Over 20,000 real world airports included in the full [[scenery]] set. The recent world scenery version 2 brought many major improvements, including more detailed heightmaps and man-made features such as roads, rivers, and train tracks.
* Correct runway markings, runway lighting, and approach lighting.
* Detailed taxiways available for many airports.
* Sloping runways.
* Airport beacon lights with rotating beacons.
* Accurate worldwide terrain based on the most recently released SRTM terrain data. 3 arc second resolution (about 90m spacing) for North and South America, Europe, Asia, Africa, and Australia.
* Roads, rivers, and train tracks.
* Realistic night lighting with lit urban areas and headlights on roads.

Real world tower registration data was used to locate towers in the United States. The data was sourced from the United States Federal Communications Commission tower registration database.

Over one million objects have been added to the [http://scenemodels.flightgear.org/ FlightGear Scenery Database].

To download scenery for the entire world as you fly over it, open the File > Scenery Download menu and check "Enable automatic download/update".

== Weather ==

[[File:Local_weather_1.00_06.jpg|center|[[Advanced weather]].|800px]]

With [[Advanced weather]], cloud patterns and winds will change throughout the day. With [[atmospheric light scattering]] enabled, fog and clouds are more realistic, and lighting changes throughout the day and during overcast periods. Advanced weather can be driven with live [[METAR]] data or manually configured for specific weather scenarios.

Enable advanced weather in the Environment > Weather dialog.

<gallery mode="packed">
File:Cloud patterns with ALS lighting.png|Advanced weather creates realistic cloud patterns that mimic the real world weather
File:Moist air and haze seen from a Boeing 707 cockpit.png|Haze and dust particles with realistic blue color in distance
File:Morning flight.jpg|Few remaining clouds in morning sunlight, looks like it will be a nice flying day!

== Rendering ==

[[Atmospheric light scattering]], or ALS, features a realistic skydome and properly lit terrain, in addition to detailed terrain texturing and trees swaying in the wind. With advanced weather enabled as well, cloud shadows and volumetric fog are also fully supported. It can be enabled via the View > Rendering Options menu. Be sure to check out the quality slider, and if you're adventurous, enable custom settings.

[[Rembrandt]] is FlightGear's shadow and lighting engine; with Rembrandt enabled, realistic shadows and lighting are possible. Note that not all aircraft support Rembrandt yet. In addition, it's not possible to use Rembrandt in conjunction with ALS. Rembrant is enabled with the <tt>--enable-rembrandt</tt> [[Command line options|command line option]].

== Sky ==

<gallery mode="packed">
File:Southwest09.jpg|
File:Water-sky01.jpg|
File:Rayleigh_blue.jpg|
File:Tree02.jpg|
</gallery>

FlightGear's night sky features accurate placement and lighting of stars, planets, and the moon.

Atmospheric light scattering features accurate lighting of the sky and terrain; in addition, oceans and rivers are realistically shaded with ripples and sun reflections. Rayleigh scattering of distant terrain is supported, tinting the ground blue or red depending on the sun angle. With random trees, tree shadows are available; experimental aircraft ground shadows are also available.

File:Morning flight.jpg

2015-03-13T07:23:36Z

Tigert: User created page with UploadWizard

=={{int:filedesc}}==
{{Information
|description={{en|1=Few remaining clouds in morning sunlight, looks like it will be a nice flying day!}}
|date=2015-03-13 09:20:38
|source={{own}}
|author=[[User:Tigert|tigert]]
|permission=
|other versions=
}}

=={{int:license-header}}==
{{self|cc-by-sa-4.0}}

[[Category:Weather]]

Realism

2015-03-13T07:17:50Z

Tigert: /* Weather */

{{cleanup}}

How realistic is [[FlightGear]]'s [[aircraft]] and environment? What is needed to get more realism and immersion from the FlightGear environment?

== Aircraft ==

[[File:DR400_Dauphin_Rembrandt_02.jpg|800px|center|The [[DR400|DR400 Dauphin]].]]

The underlying instrumentation models are very accurate, with many physical effects accounted for.

* The heading indicator has a small delay when it's slewing to your heading.
* The artificial horizon can tumble.
* The magnetic compass will rotate in all three axes and get stuck if the aircraft is tilted.
* The altimeter uses air pressure to determine altitude; if the sea level air pressure is set incorrectly, it will display the wrong altitude as in real life.
* All of the instruments that need engine power in real life are tied to the virtual engine; if the engine is not running, all vacuum-powered instruments (such as the artificial horizon and the heading indicator) will not function properly.
* Some aircraft feature accurate electrical systems with batteries that will drain over time and instruments that need electricity.

== Flight dynamics ==

Since FlightGear uses many [[FDM|flight dynamics models]] under the hood, including [[YASim]] and [[JSBSim]], the realism of an aircraft depends on its FDM. Both of these support winds and turbulence; YASim generally has more realistic ground interactions with different surfaces, while JSBSim FDMs are generally truer to the real-life aircraft. It's important to note that both of these can produce similar results if the FDM is worked on enough.

== Scenery==

<gallery mode="packed">
File:Southwest04.jpg|
File:Kansas_Scenery_Two.jpg|
</gallery>

* Over 20,000 real world airports included in the full [[scenery]] set. The recent world scenery version 2 brought many major improvements, including more detailed heightmaps and man-made features such as roads, rivers, and train tracks.
* Correct runway markings, runway lighting, and approach lighting.
* Detailed taxiways available for many airports.
* Sloping runways.
* Airport beacon lights with rotating beacons.
* Accurate worldwide terrain based on the most recently released SRTM terrain data. 3 arc second resolution (about 90m spacing) for North and South America, Europe, Asia, Africa, and Australia.
* Roads, rivers, and train tracks.
* Realistic night lighting with lit urban areas and headlights on roads.

Real world tower registration data was used to locate towers in the United States. The data was sourced from the United States Federal Communications Commission tower registration database.

Over one million objects have been added to the [http://scenemodels.flightgear.org/ FlightGear Scenery Database].

To download scenery for the entire world as you fly over it, open the File > Scenery Download menu and check "Enable automatic download/update".

== Weather ==

[[File:Local_weather_1.00_06.jpg|center|[[Advanced weather]].|800px]]

With [[Advanced weather]], cloud patterns and winds will change throughout the day. With [[atmospheric light scattering]] enabled, fog and clouds are more realistic, and lighting changes throughout the day and during overcast periods. Advanced weather can be driven with live [[METAR]] data or manually configured for specific weather scenarios.

Enable advanced weather in the Environment > Weather dialog.

<gallery mode="packed">
File:Cloud patterns with ALS lighting.png|Advanced weather creates realistic cloud patterns that mimic the real world weather
File:Moist air and haze seen from a Boeing 707 cockpit.png|Haze and dust particles with realistic blue color in distance
</gallery>

== Rendering ==

[[Atmospheric light scattering]], or ALS, features a realistic skydome and properly lit terrain, in addition to detailed terrain texturing and trees swaying in the wind. With advanced weather enabled as well, cloud shadows and volumetric fog are also fully supported. It can be enabled via the View > Rendering Options menu. Be sure to check out the quality slider, and if you're adventurous, enable custom settings.

[[Rembrandt]] is FlightGear's shadow and lighting engine; with Rembrandt enabled, realistic shadows and lighting are possible. Note that not all aircraft support Rembrandt yet. In addition, it's not possible to use Rembrandt in conjunction with ALS. Rembrant is enabled with the <tt>--enable-rembrandt</tt> [[Command line options|command line option]].

== Sky ==

<gallery mode="packed">
File:Southwest09.jpg|
File:Water-sky01.jpg|
File:Rayleigh_blue.jpg|
File:Tree02.jpg|
</gallery>

FlightGear's night sky features accurate placement and lighting of stars, planets, and the moon.

Atmospheric light scattering features accurate lighting of the sky and terrain; in addition, oceans and rivers are realistically shaded with ripples and sun reflections. Rayleigh scattering of distant terrain is supported, tinting the ground blue or red depending on the sun angle. With random trees, tree shadows are available; experimental aircraft ground shadows are also available.

Realism

2015-03-13T07:15:47Z

Tigert: /* Weather */ oops this works nicer with the layout, and easier to add more examples if someone has nice ones!

{{cleanup}}

How realistic is [[FlightGear]]'s [[aircraft]] and environment? What is needed to get more realism and immersion from the FlightGear environment?

== Aircraft ==

[[File:DR400_Dauphin_Rembrandt_02.jpg|800px|center|The [[DR400|DR400 Dauphin]].]]

The underlying instrumentation models are very accurate, with many physical effects accounted for.

* The heading indicator has a small delay when it's slewing to your heading.
* The artificial horizon can tumble.
* The magnetic compass will rotate in all three axes and get stuck if the aircraft is tilted.
* The altimeter uses air pressure to determine altitude; if the sea level air pressure is set incorrectly, it will display the wrong altitude as in real life.
* All of the instruments that need engine power in real life are tied to the virtual engine; if the engine is not running, all vacuum-powered instruments (such as the artificial horizon and the heading indicator) will not function properly.
* Some aircraft feature accurate electrical systems with batteries that will drain over time and instruments that need electricity.

== Flight dynamics ==

Since FlightGear uses many [[FDM|flight dynamics models]] under the hood, including [[YASim]] and [[JSBSim]], the realism of an aircraft depends on its FDM. Both of these support winds and turbulence; YASim generally has more realistic ground interactions with different surfaces, while JSBSim FDMs are generally truer to the real-life aircraft. It's important to note that both of these can produce similar results if the FDM is worked on enough.

== Scenery==

<gallery mode="packed">
File:Southwest04.jpg|
File:Kansas_Scenery_Two.jpg|
</gallery>

* Over 20,000 real world airports included in the full [[scenery]] set. The recent world scenery version 2 brought many major improvements, including more detailed heightmaps and man-made features such as roads, rivers, and train tracks.
* Correct runway markings, runway lighting, and approach lighting.
* Detailed taxiways available for many airports.
* Sloping runways.
* Airport beacon lights with rotating beacons.
* Accurate worldwide terrain based on the most recently released SRTM terrain data. 3 arc second resolution (about 90m spacing) for North and South America, Europe, Asia, Africa, and Australia.
* Roads, rivers, and train tracks.
* Realistic night lighting with lit urban areas and headlights on roads.

Real world tower registration data was used to locate towers in the United States. The data was sourced from the United States Federal Communications Commission tower registration database.

Over one million objects have been added to the [http://scenemodels.flightgear.org/ FlightGear Scenery Database].

To download scenery for the entire world as you fly over it, open the File > Scenery Download menu and check "Enable automatic download/update".

== Weather ==

[[File:Local_weather_1.00_06.jpg|center|[[Advanced weather]].|800px]]

With [[Advanced weather]], cloud patterns and winds will change throughout the day. With [[atmospheric light scattering]] enabled, fog and clouds are more realistic, and lighting changes throughout the day and during overcast periods. Advanced weather can be driven with live [[METAR]] data or manually configured for specific weather scenarios.

Enable advanced weather in the Environment > Weather dialog.

<gallery>
File:Cloud patterns with ALS lighting.png|Advanced weather creates realistic cloud patterns that mimic the real world weather
File:Moist air and haze seen from a Boeing 707 cockpit.png|Haze and dust particles with realistic blue color in distance
</gallery>

== Rendering ==

[[Atmospheric light scattering]], or ALS, features a realistic skydome and properly lit terrain, in addition to detailed terrain texturing and trees swaying in the wind. With advanced weather enabled as well, cloud shadows and volumetric fog are also fully supported. It can be enabled via the View > Rendering Options menu. Be sure to check out the quality slider, and if you're adventurous, enable custom settings.

[[Rembrandt]] is FlightGear's shadow and lighting engine; with Rembrandt enabled, realistic shadows and lighting are possible. Note that not all aircraft support Rembrandt yet. In addition, it's not possible to use Rembrandt in conjunction with ALS. Rembrant is enabled with the <tt>--enable-rembrandt</tt> [[Command line options|command line option]].

== Sky ==

<gallery mode="packed">
File:Southwest09.jpg|
File:Water-sky01.jpg|
File:Rayleigh_blue.jpg|
File:Tree02.jpg|
</gallery>

FlightGear's night sky features accurate placement and lighting of stars, planets, and the moon.

Atmospheric light scattering features accurate lighting of the sky and terrain; in addition, oceans and rivers are realistically shaded with ripples and sun reflections. Rayleigh scattering of distant terrain is supported, tinting the ground blue or red depending on the sun angle. With random trees, tree shadows are available; experimental aircraft ground shadows are also available.

Realism

2015-03-13T07:12:57Z

Tigert: /* Weather */ added two screenshots, thumbnailed one to make them fit in the layout better

{{cleanup}}

How realistic is [[FlightGear]]'s [[aircraft]] and environment? What is needed to get more realism and immersion from the FlightGear environment?

== Aircraft ==

[[File:DR400_Dauphin_Rembrandt_02.jpg|800px|center|The [[DR400|DR400 Dauphin]].]]

The underlying instrumentation models are very accurate, with many physical effects accounted for.

* The heading indicator has a small delay when it's slewing to your heading.
* The artificial horizon can tumble.
* The magnetic compass will rotate in all three axes and get stuck if the aircraft is tilted.
* The altimeter uses air pressure to determine altitude; if the sea level air pressure is set incorrectly, it will display the wrong altitude as in real life.
* All of the instruments that need engine power in real life are tied to the virtual engine; if the engine is not running, all vacuum-powered instruments (such as the artificial horizon and the heading indicator) will not function properly.
* Some aircraft feature accurate electrical systems with batteries that will drain over time and instruments that need electricity.

== Flight dynamics ==

Since FlightGear uses many [[FDM|flight dynamics models]] under the hood, including [[YASim]] and [[JSBSim]], the realism of an aircraft depends on its FDM. Both of these support winds and turbulence; YASim generally has more realistic ground interactions with different surfaces, while JSBSim FDMs are generally truer to the real-life aircraft. It's important to note that both of these can produce similar results if the FDM is worked on enough.

== Scenery==

<gallery mode="packed">
File:Southwest04.jpg|
File:Kansas_Scenery_Two.jpg|
</gallery>

* Over 20,000 real world airports included in the full [[scenery]] set. The recent world scenery version 2 brought many major improvements, including more detailed heightmaps and man-made features such as roads, rivers, and train tracks.
* Correct runway markings, runway lighting, and approach lighting.
* Detailed taxiways available for many airports.
* Sloping runways.
* Airport beacon lights with rotating beacons.
* Accurate worldwide terrain based on the most recently released SRTM terrain data. 3 arc second resolution (about 90m spacing) for North and South America, Europe, Asia, Africa, and Australia.
* Roads, rivers, and train tracks.
* Realistic night lighting with lit urban areas and headlights on roads.

Real world tower registration data was used to locate towers in the United States. The data was sourced from the United States Federal Communications Commission tower registration database.

Over one million objects have been added to the [http://scenemodels.flightgear.org/ FlightGear Scenery Database].

To download scenery for the entire world as you fly over it, open the File > Scenery Download menu and check "Enable automatic download/update".

== Weather ==

[[File:Local_weather_1.00_06.jpg|thumb|Advanced weather with cloud patterns]]

[[File:Cloud patterns with ALS lighting.png|thumb|Advanced weather creates realistic cloud patterns that mimic the real world weather]]
[[File:Moist air and haze seen from a Boeing 707 cockpit.png|thumb|Haze and dust particles with realistic blue color in distance]]

With [[Advanced weather]], cloud patterns and winds will change throughout the day. With [[atmospheric light scattering]] enabled, fog and clouds are more realistic, and lighting changes throughout the day and during overcast periods. Advanced weather can be driven with live [[METAR]] data or manually configured for specific weather scenarios.

Enable advanced weather in the Environment > Weather dialog.

== Rendering ==

[[Atmospheric light scattering]], or ALS, features a realistic skydome and properly lit terrain, in addition to detailed terrain texturing and trees swaying in the wind. With advanced weather enabled as well, cloud shadows and volumetric fog are also fully supported. It can be enabled via the View > Rendering Options menu. Be sure to check out the quality slider, and if you're adventurous, enable custom settings.

[[Rembrandt]] is FlightGear's shadow and lighting engine; with Rembrandt enabled, realistic shadows and lighting are possible. Note that not all aircraft support Rembrandt yet. In addition, it's not possible to use Rembrandt in conjunction with ALS. Rembrant is enabled with the <tt>--enable-rembrandt</tt> [[Command line options|command line option]].

== Sky ==

<gallery mode="packed">
File:Southwest09.jpg|
File:Water-sky01.jpg|
File:Rayleigh_blue.jpg|
File:Tree02.jpg|
</gallery>

FlightGear's night sky features accurate placement and lighting of stars, planets, and the moon.

Atmospheric light scattering features accurate lighting of the sky and terrain; in addition, oceans and rivers are realistically shaded with ripples and sun reflections. Rayleigh scattering of distant terrain is supported, tinting the ground blue or red depending on the sun angle. With random trees, tree shadows are available; experimental aircraft ground shadows are also available.

File:Moist air and haze seen from a Boeing 707 cockpit.png

2015-03-13T07:05:05Z

Tigert: User created page with UploadWizard

=={{int:filedesc}}==
{{Information
|description={{en|1=Haze and dust particles with realistic blue color in distance}}
|date=2015-03-13 09:00:59
|source={{own}}
|author=[[User:Tigert|tigert]]
|permission=
|other versions=
}}

=={{int:license-header}}==
{{self|cc-by-sa-4.0}}

[[Category:Weather]]

File:Cloud patterns with ALS lighting.png

2015-03-13T07:04:54Z

Tigert: User created page with UploadWizard

=={{int:filedesc}}==
{{Information
|description={{en|1=Advanced weather creates realistic cloud patterns that mimic the real world weather}}
|date=2015-03-13 08:59:43
|source={{own}}
|author=[[User:Tigert|tigert]]
|permission=
|other versions=
}}

=={{int:license-header}}==
{{self|cc-by-sa-4.0}}

[[Category:Weather]]

OpenSceneGraph

2015-02-17T10:18:19Z

Tigert: one closing strike tag was missing a slash, wreaking havoc..

[[File:Flightgear uml associations class diagram.png|thumb|270px|An [[UML Diagrams|UML]] class diagram disclosing the associations between some classes of the FlightGear source code.]]

= Downloading OpenSceneGraph =

'''The latest stable release of OpenSceneGraph is recommended for building FlightGear from git.'''

You should use the unstable development releases (or build OSG from git) only if you intend to develop FlightGear against new features under development in OpenSceneGraph. For all other cases the latest stable release of OpenSceneGraph is usually the best option.

== Downloading Stable OpenSceneGraph ==
The OpenSceneGraph project uses [http://svnbook.red-bean.com/nightly/en/index.html Subversion (SVN)] to distribute their sources.

'''Note''': The source code should not be downloaded to the build.osg directory, or the build will not work correctly. See below.

To download the '''latest stable version''' of OpenSceneGraph use:

svn checkout http://svn.openscenegraph.org/osg/OpenSceneGraph/tags/OpenSceneGraph-3.0.1 OpenSceneGraph

'''Manual Download''': If you don't want to use SVN, you can also pick a stable release from the OSG download page:

http://www.openscenegraph.org/projects/osg/wiki/Downloads

If the main OSG site is down (frequently) you can also use one of its various mirrors:

http://www.freebsd.org/cgi/pds.cgi?ports/graphics/osg

== OpenSceneGraph developer versions ==
FlightGear developers may want to use a '''development release''' of OpenSceneGraph:

svn checkout http://svn.openscenegraph.org/osg/OpenSceneGraph/tags/OpenSceneGraph-3.1.6 OpenSceneGraph

You can replace the "3.1.6" by future development OSG versions (if known to be compatible with FlightGear).

Alternatively, developers interested in '''today's OSG development''' can download the current OSG trunk.

'''WARNING''': The sources of current OSG development aren't always compatible with FlightGear. Only use these if you're interested in OSG development or developing new OSG features for FlightGear:

svn checkout http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk OpenSceneGraph

= Compiling OpenSceneGraph =

OpenSceneGraph uses cmake. Since OSG version 2.7.3 (8th Oct 2008) a relatively new version of cmake is required. According to OSGs CMakeLists.txt it's 2.6.1 but cmake 2.6.0-5 from [http://backports.org/dokuwiki/doku.php backports.org] for Debian/Etch does the trick.
It's also possible to comment out lines 25 to 27 in OSGs CMakeLists.txt:
# if(POLICY CMP0008)
# cmake_policy(SET CMP0008 OLD)
# endif(POLICY CMP0008)

A minimal build instruction for unix systems is

mkdir build.osg
cd build.osg
cmake ../path/to/osg/source
make
make install

On other systems the steps might be different.

Recommended options to set in the cmake menus:
* Build type: Release
* You don't need to build the examples, wrappers or applications.

== Installing OpenSceneGraph and FlightGear with --prefix ==

If you use --prefix to choose were to install FlightGear and do not want to install OSG globally on the system this can be done with the following method:

OpenSceneGraph uses cmake so to build it do

mkdir build.osg
cd build.osg
cmake -D CMAKE_BUILD_TYPE="Release" -D CMAKE_CXX_FLAGS_RELEASE="-O3 -pipe" -D CMAKE_C_FLAGS_RELEASE="-O3 -pipe" \
-D CMAKE_INSTALL_PREFIX:PATH="${MY_PREFIX}" ../path/to/osg/source
make
make install

or if you want to avoid needing to set LD_LIBRARY_PATH

mkdir build.osg
cd build.osg
cmake -D CMAKE_BUILD_TYPE="Release" -D CMAKE_CXX_FLAGS_RELEASE="-O3 -pipe" -D CMAKE_C_FLAGS_RELEASE="-O3 -pipe" \
-D CMAKE_INSTALL_PREFIX:PATH="${MY_PREFIX}" -D CMAKE_INSTALL_RPATH_USE_LINK_PATH:BOOLEAN="true" ../path/to/osg/source
make
make install

Configure and build SimGear and FlightGear with --prefix as usual.

No need to install any quickly changing software globally.

Installing with --prefix is a very nice way to keep several distinct and independent versions of FlightGear around. To start a new $PREFIX directory you'll also need to install plib in it, but that is easy. Most other needed dependencies are usually available through the package system of most Linux distributions (e.g. FreeGLUT, SDL, ALSA, etc).

== lib64 ==
Content moved to [[Talk:OpenSceneGraph]] for now.

= Features and issues =

Historically FlightGear has used [[PLIB]] instead of '''OpenSceneGraph'''. [[FlightGear 1.9.0]], released Decemeber 22, 2008, marked the release of the OSG version of FlightGear. While much of the conversion to OSG has happened over the years, [[PLIB]] is still used for some functions.

Thanks to Mathias Fröhlich and Tim Moore, we can use recent OpenSceneGraph releases.

== Regressions in CVS/HEAD ==
This section is meant to always remain up to date with the latest version in CVS/HEAD, please make sure to add/delete items as necessary.
* feature to disable scenery rendering via /sim/rendering/draw-otw property is not working at the moment (11/2008)

== Current issues (very out of date) ==

* <strike>The 2D Panels and the rendering order of instruments ... is wrong.</strike>

* transparency issues:
** <strike>runway lights shine through panel:</strike>
** runway lights shine through cloud layers in an awkward way:
** 2D-cloud layers flood into cockpit
** The prop of the C172 block the view on the waves of the carrier
** The reflector gun sight on the Seahawk causes other transparent objects (carrier wake etc.) to disappear
** A new overhead window in the C172 (inside out)

* <strike>Runway lighting seems to have rendering artefacts on ATI Cards.</strike>

* <strike>Enhanced runway lighting option in the drop-down menu seems to have no effect - light always appear enhanced.</strike>

* <strike>Seneca II HSI: upper instrument clipping issue for NAV/HDG flags, heading bug, pointer</strike>

[[List of 'compatible' aircraft]] TO BE CONTINUED ('''NOTE:''' the list is out of date.)

== Missing features ==
Due to the migration from PLIB to OSG, some of the features seen in past versions of FlightGear are now temporarily non-functional. These are:

* <strike>3D clouds</strike> 3D clouds back thanks to Stuart Buchanan still have some visual artifacts

* <strike>Rendering of some scenes is not perfect.</strike>

* Shadows

* Exhaust shader

* Weather Radar is not showing any clouds

* cloud layers don't follow the curve of the earth

* Menu Items have no effect
** Enhanced Runway Lights
** Bump Mapped Clouds

== Miscellaneous OSG benefits ==
* Models and scenery load in a separate thread
* Tree shaders allow "forests" of trees
* Improved precipitation modeling
* "Pick" animations enable greater realism and ease of creation for 3D cockpits
* Multi-monitor views

Mathias: "I think that we should make use in the longer term of the Producers
capabilities for multiple view installations.
But not only multipipe installs will benefit from that. The Producer will also
help to get benefit from multicore SMP machines.
For that the following article is of huge interest:
http://www.donburns.net/OSG/Articles/OSGMP/"

= Getting the PLIB Code =

Use the tag <tt>PRE_OSG_PLIB_20061029</tt> for checking out the branch with the plib scenegraph.

For SimGear, this works (more or less) as follows:

'''cvs -d :pserver:cvsguest@cvs.simgear.org:/var/cvs/SimGear-0.3 login'''
'''CVS passwd: guest'''
'''cvs -d :pserver:cvsguest@cvs.simgear.org:/var/cvs/SimGear-0.3 co source'''
'''cd source'''
'''cvs up -rPRE_OSG_PLIB_20061029'''

For FlightGear, you have to update the "source" directory:

'''cvs -d :pserver:cvsguest@cvs.flightgear.org:/var/cvs/FlightGear-0.9 login'''
'''CVS passwd: guest'''
'''cvs -d :pserver:cvsguest@cvs.flightgear.org:/var/cvs/FlightGear-0.9 co -rPRE_OSG_PLIB_20061029 source
'''
The data directory should be the CVS HEAD version. Some aircraft, however, have a PRE_OSG_PLIB_20061029 branch that works better with FlightGear/plib, e.g Hawker Hunter.

= External link =
* http://www.openscenegraph.org/

{{Building}}

[[Category:Software]]

OpenSceneGraph

2015-02-17T08:07:24Z

Tigert: updated to point out latest OSG stable as the best choice for most cases, moved plib chapter into features and issues, out of the way from the beginning.

[[File:Flightgear uml associations class diagram.png|thumb|270px|An [[UML Diagrams|UML]] class diagram disclosing the associations between some classes of the FlightGear source code.]]

= Downloading OpenSceneGraph =

'''The latest stable release of OpenSceneGraph is recommended for building FlightGear from git.'''

You should use the unstable development releases (or build OSG from git) only if you intend to develop FlightGear against new features under development in OpenSceneGraph. For all other cases the latest stable release of OpenSceneGraph is usually the best option.

== Downloading Stable OpenSceneGraph ==
The OpenSceneGraph project uses [http://svnbook.red-bean.com/nightly/en/index.html Subversion (SVN)] to distribute their sources.

'''Note''': The source code should not be downloaded to the build.osg directory, or the build will not work correctly. See below.

To download the '''latest stable version''' of OpenSceneGraph use:

svn checkout http://svn.openscenegraph.org/osg/OpenSceneGraph/tags/OpenSceneGraph-3.0.1 OpenSceneGraph

'''Manual Download''': If you don't want to use SVN, you can also pick a stable release from the OSG download page:

http://www.openscenegraph.org/projects/osg/wiki/Downloads

If the main OSG site is down (frequently) you can also use one of its various mirrors:

http://www.freebsd.org/cgi/pds.cgi?ports/graphics/osg

== OpenSceneGraph developer versions ==
FlightGear developers may want to use a '''development release''' of OpenSceneGraph:

svn checkout http://svn.openscenegraph.org/osg/OpenSceneGraph/tags/OpenSceneGraph-3.1.6 OpenSceneGraph

You can replace the "3.1.6" by future development OSG versions (if known to be compatible with FlightGear).

Alternatively, developers interested in '''today's OSG development''' can download the current OSG trunk.

'''WARNING''': The sources of current OSG development aren't always compatible with FlightGear. Only use these if you're interested in OSG development or developing new OSG features for FlightGear:

svn checkout http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk OpenSceneGraph

= Compiling OpenSceneGraph =

OpenSceneGraph uses cmake. Since OSG version 2.7.3 (8th Oct 2008) a relatively new version of cmake is required. According to OSGs CMakeLists.txt it's 2.6.1 but cmake 2.6.0-5 from [http://backports.org/dokuwiki/doku.php backports.org] for Debian/Etch does the trick.
It's also possible to comment out lines 25 to 27 in OSGs CMakeLists.txt:
# if(POLICY CMP0008)
# cmake_policy(SET CMP0008 OLD)
# endif(POLICY CMP0008)

A minimal build instruction for unix systems is

mkdir build.osg
cd build.osg
cmake ../path/to/osg/source
make
make install

On other systems the steps might be different.

Recommended options to set in the cmake menus:
* Build type: Release
* You don't need to build the examples, wrappers or applications.

== Installing OpenSceneGraph and FlightGear with --prefix ==

If you use --prefix to choose were to install FlightGear and do not want to install OSG globally on the system this can be done with the following method:

OpenSceneGraph uses cmake so to build it do

mkdir build.osg
cd build.osg
cmake -D CMAKE_BUILD_TYPE="Release" -D CMAKE_CXX_FLAGS_RELEASE="-O3 -pipe" -D CMAKE_C_FLAGS_RELEASE="-O3 -pipe" \
-D CMAKE_INSTALL_PREFIX:PATH="${MY_PREFIX}" ../path/to/osg/source
make
make install

or if you want to avoid needing to set LD_LIBRARY_PATH

mkdir build.osg
cd build.osg
cmake -D CMAKE_BUILD_TYPE="Release" -D CMAKE_CXX_FLAGS_RELEASE="-O3 -pipe" -D CMAKE_C_FLAGS_RELEASE="-O3 -pipe" \
-D CMAKE_INSTALL_PREFIX:PATH="${MY_PREFIX}" -D CMAKE_INSTALL_RPATH_USE_LINK_PATH:BOOLEAN="true" ../path/to/osg/source
make
make install

Configure and build SimGear and FlightGear with --prefix as usual.

No need to install any quickly changing software globally.

Installing with --prefix is a very nice way to keep several distinct and independent versions of FlightGear around. To start a new $PREFIX directory you'll also need to install plib in it, but that is easy. Most other needed dependencies are usually available through the package system of most Linux distributions (e.g. FreeGLUT, SDL, ALSA, etc).

== lib64 ==
Content moved to [[Talk:OpenSceneGraph]] for now.

= Features and issues =

Historically FlightGear has used [[PLIB]] instead of '''OpenSceneGraph'''. [[FlightGear 1.9.0]], released Decemeber 22, 2008, marked the release of the OSG version of FlightGear. While much of the conversion to OSG has happened over the years, [[PLIB]] is still used for some functions.

Thanks to Mathias Fröhlich and Tim Moore, we can use recent OpenSceneGraph releases.

== Regressions in CVS/HEAD ==
This section is meant to always remain up to date with the latest version in CVS/HEAD, please make sure to add/delete items as necessary.
* feature to disable scenery rendering via /sim/rendering/draw-otw property is not working at the moment (11/2008)

== Current issues (very out of date) ==

* <strike>The 2D Panels and the rendering order of instruments ... is wrong.</strike>

* transparency issues:
** <strike>runway lights shine through panel:</strike>
** runway lights shine through cloud layers in an awkward way:
** 2D-cloud layers flood into cockpit
** The prop of the C172 block the view on the waves of the carrier
** The reflector gun sight on the Seahawk causes other transparent objects (carrier wake etc.) to disappear
** A new overhead window in the C172 (inside out)

* <strike>Runway lighting seems to have rendering artefacts on ATI Cards.<strike>

* <strike>Enhanced runway lighting option in the drop-down menu seems to have no effect - light always appear enhanced.</strike>

* <strike>Seneca II HSI: upper instrument clipping issue for NAV/HDG flags, heading bug, pointer</strike>

[[List of 'compatible' aircraft]] TO BE CONTINUED ('''NOTE:''' the list is out of date.)

== Missing features ==
Due to the migration from PLIB to OSG, some of the features seen in past versions of FlightGear are now temporarily non-functional. These are:

* <strike>3D clouds</strike> 3D clouds back thanks to Stuart Buchanan still have some visual artifacts

* <strike>Rendering of some scenes is not perfect.</strike>

* Shadows

* Exhaust shader

* Weather Radar is not showing any clouds

* cloud layers don't follow the curve of the earth

* Menu Items have no effect
** Enhanced Runway Lights
** Bump Mapped Clouds

== Miscellaneous OSG benefits ==
* Models and scenery load in a separate thread
* Tree shaders allow "forests" of trees
* Improved precipitation modeling
* "Pick" animations enable greater realism and ease of creation for 3D cockpits
* Multi-monitor views

Mathias: "I think that we should make use in the longer term of the Producers
capabilities for multiple view installations.
But not only multipipe installs will benefit from that. The Producer will also
help to get benefit from multicore SMP machines.
For that the following article is of huge interest:
http://www.donburns.net/OSG/Articles/OSGMP/"

= Getting the PLIB Code =

Use the tag <tt>PRE_OSG_PLIB_20061029</tt> for checking out the branch with the plib scenegraph.

For SimGear, this works (more or less) as follows:

'''cvs -d :pserver:cvsguest@cvs.simgear.org:/var/cvs/SimGear-0.3 login'''
'''CVS passwd: guest'''
'''cvs -d :pserver:cvsguest@cvs.simgear.org:/var/cvs/SimGear-0.3 co source'''
'''cd source'''
'''cvs up -rPRE_OSG_PLIB_20061029'''

For FlightGear, you have to update the "source" directory:

'''cvs -d :pserver:cvsguest@cvs.flightgear.org:/var/cvs/FlightGear-0.9 login'''
'''CVS passwd: guest'''
'''cvs -d :pserver:cvsguest@cvs.flightgear.org:/var/cvs/FlightGear-0.9 co -rPRE_OSG_PLIB_20061029 source
'''
The data directory should be the CVS HEAD version. Some aircraft, however, have a PRE_OSG_PLIB_20061029 branch that works better with FlightGear/plib, e.g Hawker Hunter.

= External link =
* http://www.openscenegraph.org/

{{Building}}

[[Category:Software]]

Snow

2012-01-14T21:12:42Z

Tigert: /* Rough and Dirty ideas */

{{WIP}}
[[File:SnowAtAltitude2.jpg|thumb|270px|The snow line in FlightGear 2.0.0.]]
As of [[FlightGear]] 2.6.0, the '''snow line''' is based on a user selectable elevation (<tt>Environment > Global Weather</tt> dialog) and the nearest [[METAR]] station's report. If the METAR reports snow and the station is below the level set by the user, the snow line will be set to the station's altitude.

Altough this is better than the former behaviour (only user setting), it's still not realistic. The purpose of this document is to collect ideas and info on how to automate the snow line calculations.

== Snow line ==
There are two definitions of snow line:
* [[#Climatic|Climatic]]: the point above which snow and ice cover the ground throughout the year.<ref>[http://en.wikipedia.org/wiki/Snow_line Snow line] (Wikipedia)</ref>
* [[#Actual|Actual]]: the actual point at which snow is currently present. In summer, this is often equal to the climatic snow line.

=== Climatic ===
[[File:Climatic snow line.png|thumb|270px]]
Based on the climatic snow line values given at [http://en.wikipedia.org/wiki/Snow_line Wikipedia], we can estimate the climatic snow line at every latitude with the following formula:

0.0001*lat4 - 0.0019*lat3 - 1.7972*lat2 + 15.444*lat + 6022.1

In [[Nasal]] this will be:
var lat = getprop("/position/latitude-deg");
var snowLineClimatic = 0.0001*math.pow(lat,4) - 0.0019*math.pow(lat,3) - 1.7972*math.pow(lat,2) + 15.444*lat + 6022.1;

=== Actual ===

== Airports ==
A SNOWTAM is a message describing the conditions of the runways, taxiways and apron at an aerodrome. During the winter season a SNOWTAM will be issued each day in the morning, before flying starts. A SNOWTAM is valid for 24 hours, but there are rules stating that a new SNOWTAM shall be issued sooner if significant changes occur.<ref>[http://www.baseops.de/snowtam.php HowTo decode a SNOWTAM]</ref>

As of 2.6.0, FlightGear has a runway [[shader]] to make it look wet during rain showers. This could be easily adapted to read SNOWTAM data.

== Rough and Dirty ideas ==

Since snowtam and metar snow report consider mostly the runway, and there can be snow on the ground even if the runway is dry and clear (sunny spring days for example) there could be a method to get a rough idea whether there is snow on the ground at a given location and certain time of year.

Maybe an idea worth poking at would be some kind of geometrical lat/lon grid matrix for each month (or week?) of the year with either boolean value (snow / no snow) or perhaps something like 8 probability levels. 0 would be no snow, 8 would be total snow coverage, and the values in between could be for example implemented as somewhat randomized probability of snow, taking current METAR into account. Like, value of 1 would give you snow if temperature is below freezing and there is rain / snow in METAR. Value of 7 would give snow as long as temperature is not too warm, or something like that.

This might give us somewhat reasonable winter/snow season globally at most locations with reasonable effort..?

== Vegetation ==
At the moment, FlightGear cannot change <tt>materials.xml</tt> (and thus random tree textures) on run-time from summer to winter. Ideally, the winter textures should not contain any snow, it should be added by the shader instead (so we can make use of the snow line).

== External links ==
* [http://environmentalresearchweb.org/blog/2010/08/the-snowline-its-not-a-line-st.html The snowline: it’s not a line (still less an isotherm)] (Environmental Research Web)

{{Appendix}}

Snow

2012-01-14T21:11:08Z

Tigert: added my thoughts about the snow coverage lookup matrix

{{WIP}}
[[File:SnowAtAltitude2.jpg|thumb|270px|The snow line in FlightGear 2.0.0.]]
As of [[FlightGear]] 2.6.0, the '''snow line''' is based on a user selectable elevation (<tt>Environment > Global Weather</tt> dialog) and the nearest [[METAR]] station's report. If the METAR reports snow and the station is below the level set by the user, the snow line will be set to the station's altitude.

Altough this is better than the former behaviour (only user setting), it's still not realistic. The purpose of this document is to collect ideas and info on how to automate the snow line calculations.

== Snow line ==
There are two definitions of snow line:
* [[#Climatic|Climatic]]: the point above which snow and ice cover the ground throughout the year.<ref>[http://en.wikipedia.org/wiki/Snow_line Snow line] (Wikipedia)</ref>
* [[#Actual|Actual]]: the actual point at which snow is currently present. In summer, this is often equal to the climatic snow line.

=== Climatic ===
[[File:Climatic snow line.png|thumb|270px]]
Based on the climatic snow line values given at [http://en.wikipedia.org/wiki/Snow_line Wikipedia], we can estimate the climatic snow line at every latitude with the following formula:

0.0001*lat4 - 0.0019*lat3 - 1.7972*lat2 + 15.444*lat + 6022.1

In [[Nasal]] this will be:
var lat = getprop("/position/latitude-deg");
var snowLineClimatic = 0.0001*math.pow(lat,4) - 0.0019*math.pow(lat,3) - 1.7972*math.pow(lat,2) + 15.444*lat + 6022.1;

=== Actual ===

== Airports ==
A SNOWTAM is a message describing the conditions of the runways, taxiways and apron at an aerodrome. During the winter season a SNOWTAM will be issued each day in the morning, before flying starts. A SNOWTAM is valid for 24 hours, but there are rules stating that a new SNOWTAM shall be issued sooner if significant changes occur.<ref>[http://www.baseops.de/snowtam.php HowTo decode a SNOWTAM]</ref>

As of 2.6.0, FlightGear has a runway [[shader]] to make it look wet during rain showers. This could be easily adapted to read SNOWTAM data.

== Rough and Dirty ideas ==

Since snowtam and metar snow report consider mostly the runway, and there can be snow on the ground even if the runway is dry and clear (sunny spring days for example) there could be a method to get a rough idea whether there is snow on the ground at a given location and certain time of year.

Maybe an idea worth poking at would be some kind of geometrical lat/lon grid matrix for each month (or week?) of the year with either boolean value (snow / no snow) or perhaps something like the 8 cloud coverage stages in METARs. 0 would be no snow, 8 would be total snow coverage, and the values in between could be for example implemented as somewhat randomized probability of snow, taking current METAR into account. Like, value of 1 would give you snow if temperature is below freezing and there is rain / snow in METAR. Value of 7 would give snow as long as temperature is not too warm, or something like that.

This might give us somewhat reasonable winter/snow season globally at most locations with reasonable effort..?

== Vegetation ==
At the moment, FlightGear cannot change <tt>materials.xml</tt> (and thus random tree textures) on run-time from summer to winter. Ideally, the winter textures should not contain any snow, it should be added by the shader instead (so we can make use of the snow line).

== External links ==
* [http://environmentalresearchweb.org/blog/2010/08/the-snowline-its-not-a-line-st.html The snowline: it’s not a line (still less an isotherm)] (Environmental Research Web)

{{Appendix}}