Particle effects : snow and rain
  by Nicolas VIVIEN
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							Patch v5 (only test)


FEATURES :
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This patch permits to add snow and rain effects in using particle from OSG.

This improvement works with the METAR informations to enable / disable rain or snow effects.
(intensity of effects is : low, meddium, high)

The precipitations are stopped when the aircraft is above the cloud layers.

The rain preicipitation turn off snow precipitations when the ambiant temperature is lower
than the dew point temperature. (the temperature depends on altitude)

The wind influents the precipitations (speed and direction support).


CHANGELOG v5 :
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- Fixe the bug about world coordinate...
- Add rain transforming to snow with altitude and temperature...
- Add the wind feature (direction and velocity)


CHANGELOG v4 :
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- Follow the Tim'advice, Precipitation object has to link to each tile... but to the scene.
- First test with wind...


CHANGELOG v3 :
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- The origin of Precipitation object is calculate with worldcoordinate Matrix.
- Precipitations fall vertically anywhere on the earth...


CHANGELOG v2 :
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- Link the precipitation object to tile element :
Now, there is one precipitation object per tile. It permits to use the world coordinate.
- Add links between precipitation and cloud layers :
When you are above the cloud layer, the precipitations are stopped.


CHANGELOG v1 :
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Firt step : test the precipitation effect.


TO DO :
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For the next release of patch :
1) it's raining cats and dogs in my plane !!! (fixed this issue)


INSTALL :
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- You have to remove the others patch about precipitation.

- You have to add the two files :
precipitation.hxx and precipitation.cxx 
in the directory simgear/simgear/environment

- You have to apply simgear patch

- You have to add the two files :
precipitation_mgr.hxx and precipitation_mgr.cxx 
in the directory flightgear/src/Environment

- You have to apply flightgear patch

- Then, build simgear and flightgear.

