Scattering Medium: Density units?
Moderators: ChrisHekman, aoktar
Is the density field in real world units, if so what are they and can I match it to real world substances if I find the values online?
Windows 10 - 64GB RAM - Cinema 4D R20 - RTX 2070 x3
The density is actually a scale that is applied directly to the scattering and absorption coefficients, so it has no units.
It would be best to find coefficient values and apply these to scattering and absorption, leaving density at 1 unless you need to scale these values up more. Basically the effect of increasing the coefficients (black->white) is the same as increasing density.
fyi: For volumes, the density is also used to calculate emission output.
It would be best to find coefficient values and apply these to scattering and absorption, leaving density at 1 unless you need to scale these values up more. Basically the effect of increasing the coefficients (black->white) is the same as increasing density.
fyi: For volumes, the density is also used to calculate emission output.
Thanks for the info. The default value is 100, which is a little confusing. From your reply it seems it should be 1?haze wrote:The density is actually a scale that is applied directly to the scattering and absorption coefficients, so it has no units.
It would be best to find coefficient values and apply these to scattering and absorption, leaving density at 1 unless you need to scale these values up more. Basically the effect of increasing the coefficients (black->white) is the same as increasing density.
fyi: For volumes, the density is also used to calculate emission output.
The scene is liquid in a glass bottle, both materials have scattering mediums applied, though this is causing some confusing issues.
If the inner liquid has a deep red absorption value (inverted checked, so it renders red), changing the absorption of the glass changes the liquid, but not the glass.
Eg
glass absorption = 100% white, liquid is unchanged
glass absorption = 50% grey, liquid becomes almost clear, glass unchanged
this is very counter intuitive, one would expect the colours of the two objects to simply multiply (become darker, not lighter). Increasing the density of the liquid to 5 brings back the red colour, but its not at all clear why this should be so.
Even more confusing, if next I increase the glass density to 2 the liquid changes from red to green.
Windows 10 - 64GB RAM - Cinema 4D R20 - RTX 2070 x3
The default value of 100 for density was somewhat arbitrarily chosen, but mostly to suit sample volumes from openvdb.org
The second problem you mention is actually a current limitation of the renderer. The issue is that we don't currently keep track of nested dielectrics, but we are planning to do this.
At the moment, the best result you can get is if you make sure the liquid's surface is slightly embedded in the glass, but the glass is still the outermost material.
If you still have some trouble, please send me an ORBX and I'll see if I can improve it.
The second problem you mention is actually a current limitation of the renderer. The issue is that we don't currently keep track of nested dielectrics, but we are planning to do this.
At the moment, the best result you can get is if you make sure the liquid's surface is slightly embedded in the glass, but the glass is still the outermost material.
If you still have some trouble, please send me an ORBX and I'll see if I can improve it.