What's the median roughness of asphalt material?

gnoop

Megascan  does  around  0.83.   Some guides tells it's 0.76.   Chat GPT told me  0.75.    Adobe substance libraries  have a lot of  around 0.5-0.6.       Textures.com  are in range of  0.75-0.9.      It all gave pretty subtle difference in our old renderer and Megacan ones looked almost matte   and now 0.76 looks like a nuke  when the sun is around 25 degree above the skyline .

In offline renderers  it's not a big difference   especially with ACES or AgX tone mapping working .   In our new renderer  I  see very strong intensity of highlight  with low sun  and hardly anything  when the sun  goes  50 degree above the horizon with 0.83 while with Cycles, Arnold or Octane  it's still a lot of pretty noticeable wide spread highlight spot.     So I wonder what you guys do?

 

poopipe

roughness is an average over an area so there's no correct value for a surface without taking that into account.
measuring roughess and translating it into something that matches your specular model is probably all but impossible

as such  - as a surface gets further away from the viewer,  progressively larger changes in surface direction start to behave like microsurface information - which is what your roughness texture defines. 

in short - eyeball it and have some sort of toksvig roughen over distance thing going on in your materials


other things contribute to this as well - particularly with glancing light angles
dielectric reflectance and different diffuse BRDFs to name a couple

gnoop

Thanks poopipe   Yeah , I understand . Just wonder what median value people use  currently?   To see if ours are off and how much