The #1 most-asked tech support question we receive is:
“When I enable rain or snow in SilverLining, my clouds disappear!”
This falls into the categorgy of “it’s not a bug, it’s a feature.” SilverLining simulates reduced visibility in the presence of precipitation, and since the clouds are usually very far from the camera, they are often entirely obscured when you’re in the middle of heavy precipitation. We handle visibility effects on clouds by fading them out with distance, in order to ensure they blend smoothly against what may be a non-homogeneous sky behind them.
We determine the proper visibility as a function of snowfall precipitation rate using equations in the following paper:
Rasmussen, Vivekanandan, Cole, Meyers, Masters, “The Estimation of Snowfall Rate Using Visibility”, 1999, Journal of Applied Meteorology, Vol. 38, pp 1542-1563
For rain, our reference is:
Atlas, David, 1953, “Optical Extinction by Rainfall”, Journal of Meterology Vol. 10 pp 486-488.
However, many customers find our reduction in visibility to be too aggressive. There are ways to adjust it to your liking.
First, look for these settings inside the Resources/SilverLining.config file included with the SilverLining SDK:
rain-visibility-multiplier = 1.0
snow-visibility-multiplier = 3.0
sleet-visibility-multiplier = 1.0
Increasing these settings will increase the visibility for a given precipitation rate. You may also disable the effect entirely by setting:
enable-precipitation-visibility-effects = no
apply-fog-from-cloud-precipitation = no
If you do this, we do recommend that you manage your own visibility reduction in the presence of precipitation instead. Heavy rain or snow against a clear, sunny sky not only looks unnatural, it makes the precipitation particles hard to see against the bright background. Precipitation will look best with overcast conditions, when you have a stratus cloud layer in the scene with 100% coverage.
While you’re looking at SilverLining.config’s precipitation section, you’ll see there are many other settings that allow you to adjust the brightness, width, and number of particles. If you want rain particles to be more easily visible, or for precipitation to appear heavier overall, these settings will allow you to do that.
Another common question we get related to precipitation is:
Rain or snow looks fine on the front channel of my simulator, but doesn’t look right on the side channels.
SilverLining by default will try to reverse-engineer your projection matrix, in order to pull in the near clip plane to ensure precipitation particles near the camera are visible, and also to enforce a minimum particle size that will project to some minimum size in pixels. However, some exotic projection matrices on multi-channel displays can mess up our math. In this case, be sure to set your near clip plane to something close to the camera, say no more than 1 meter, and disable these effects by setting:
rain-minimum-pixels = 0
sleet-minimum-pixels = 0
snow-minimum-pixels = 0
rain-use-depth-buffer = yes
snow-use-depth-buffer = yes
sleet-use-depth-buffer = yes
That should clear it up.
SilverLining takes great care to provide physically-realistic precipitation effects, but if you need to tune them, we provide lots of ways to do so. If you need further guidance, don’t hesitate to contact firstname.lastname@example.org.