Revit PBR material parameters

[psalehishafaTRFRW]

Revit PBR material comes with roughness and reflection values which to me makes no sense at all.

Roughness and Reflectivity are opposite sides of the same material attribute. The rougher the surface the less reflective it is. Setting up the roughness image will automatically sets reflectivity of that material.

So if we are creating PBR (Physically Based Render) material, why introduce such a nonsensical parameter?

[barthbradley]

Why don't you Google it? 

https://magazine.substance3d.com/autodesk-revit-pbr-material-workflow-for-architecture/

[psalehishafaTRFRW]

Your link doesn't give any answers. I've searched the web and there is nothing out there about Revit's inclusion of both reflectivity and roughness. 

This is a very specific question and non of these websites get into actually explaining the matter in detail.

Again the question is about Reflectivity and Roughness both being included inside the parameter when they refer to the same material attribute. You should use one or the other not both.

[_Vijay]

can use according to our need.

Again the question is about Reflectivity and Roughness both being included inside the parameter when they refer to the same material attribute. You should use one or the other not both.

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[barthbradley]

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@psalehishafaTRFRW wrote:

Your link doesn't give any answers. I've searched the web and there is nothing out there about Revit's inclusion of both reflectivity and roughness. 

This is a very specific question and non of these websites get into actually explaining the matter in detail.

Again the question is about Reflectivity and Roughness both being included inside the parameter when they refer to the same material attribute. You should use one or the other not both.

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What are your credentials? I need to know before I can answer your question, so that I can speak to your level of understanding. I don't want the explanation to sound "nonsensical" to you. 

[barthbradley]

Is this understandable or too deep into the weeds?     

https://www.sharetextures.com/textures/blog/physically-based_rendering/

[psalehishafaTRFRW]

Thanks for the post barthbradley but I'm all but familiar with the basics of PBR. I'm an Arch Viz specialist and this is what I do day in day out. Still waiting to see if there is a reason behind this. The only thing I can think of is that the extra slider introduces imperfections. And if that's the case, there should be some kind of documentation for it. 

For now I really believe this to be a mistake.

[barthbradley]

https://www.autodesk.com/autodesk-university/class/PBR-Materials-Revit-What-These-Materials-Mean-and...

[lucdoucet_msdl]

@psalehishafaTRFRW 

Revit PBR material comes with roughness and reflection values which to me makes no sense at all.

Roughness and Reflectivity are opposite sides of the same material attribute. The rougher the surface the less reflective it is.

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From the Revit 2020 help on Reflectivity properties of legacy appearance assets:

https://help.autodesk.com/view/RVT/2020/ENU/?guid=GUID-95A37D82-95F9-4F8A-AD18-F17ACAF5E016

Reflectivity properties have been deprecated and replaced by the following physically based definitions in appearance assets :

Reflectance

How much light is reflected from the surface in a mirror-like fashion (specular reflectance) when looking at the surface perpendicularly.

The material will always show a high specular reflectance when viewed from grazing angles (Fresnel's effect).

Roughness

The surface finish of the material, specifying the size of microscopic imperfections.

When Roughness is defined as zero, the entire surface is a perfect mirror. Larger values tend towards more diffuse (rough) appearance and larger highlights.

Use Roughness together with Anisotropy to achieve a brushed finish.

https://help.autodesk.com/view/RVT/2020/ENU/?guid=GUID-1E0D0975-6B12-47E6-AE92-BF8E4EF70748

As I understand it, depending on the rendering shader used, Revit will use either the Roughness valueif PBR and Reflectivity value if not.

Hope this answers your question.

- luc

[barthbradley]

..or are you talking about PBR beer?   When I reflect on my college days, I do recall some rough PBR hangovers. Is this what you mean by  "Reflectivity" and "Roughness"?  😉

[psalehishafaTRFRW]

Thanks for your reply. I believe the terms used inside the appearance panel are very confusing, specially to those of us who work with PBR all the time. They are used differently within the CG community.

Greatly appreciate the response but I don't believe you are correct about the Roughness being used when PBR is being implemented and Reflectance is used when standard material is applied. 

I now believe Reflectance is the term used in Revit to refer to Gloss or Specular Highlight which would be the correct way of applying PBR textures.

[psalehishafaTRFRW]

Ok Thanks alot; as if I wasn't busy enough now I have to get some beer.

[barthbradley]

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@psalehishafaTRFRW wrote:

...Reflectance is the term used in Revit to refer to Gloss or Specular Highlight 

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EXACTLY!!!

[lucdoucet_msdl]

@psalehishafaTRFRW 

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Greatly appreciate the response but I don't believe you are correct about the Roughness being used when PBR is being implemented and Reflectance is used when standard material is applied. 

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Please note that I wrote the term Reflectivity (not Reflectance) is used in the legacy non-PBR materials.

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I now believe Reflectance is the term used in Revit to refer to Gloss or Specular Highlight which would be the correct way of applying PBR textures.

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I agree, but the term Reflectance for legacy non-PBR materials also corresponds to Gloss / Specular Highlight. Here is Revit's definition of the Reflectance parameter on the Revit Help link I sent you:

Property Description

Direct	Measurement of how much light the material reflects when the surface is directly facing the camera. Enter a value between 0 (no reflections) and 1 (maximum reflections).
Oblique	Measurement of how much light the material reflects when the surface is at an angle to the camera. Enter a value between 0 (no reflections) and 1 (maximum reflections).

I can't speak to Autodesk's choice of terminology implied in your original posting, but I think you have the answer to what the parameters in Revit's PBR materials mean.

-luc

[Adam.Nicolas.Li]

I just learned two kinds of PBR for workflow.

The first one is Metal-Roughness.

The second one is Specular-Glossiness.

But I don't know which Revit uses?

I can't match the Revit material parameters with any of the above workflows.

many thanks for your help.

[547672635]

I have encountered the same problem, did you figure it out?