Particle effects : snow and rain
  by Nicolas VIVIEN
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							First patch (only test)


FEATURES :
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This first try permits to add a basic snow and rain effects in using
particle from OSG.

For the moment, the patch uses the METAR informations to enable / disable
rain or snow effects. (intensity of effects is : low, meddium, high)


TO DO :
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For the next release of patch :
1) Add the wind direction and velocity effect
2) it's raining cats and dogs in my plane !!! (fixed this issue)
3) I want to the density of effects depend on altitude. If I'm higher than 
clouds layer, rain (or snow) is stopped...
4) The particle effects have to depend on the camera position.


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

- You have to apply simgear patch

- You have to apply flightgear patch

- Then, build simgear and flightgear.

