Any Idea about hudge blocks in Cycles rendering

Question

I imported an FBX Revit model and started to modify it a little bit. I added some textures, etc. In the first days the render was ok. today after some modifications is not. Do you have any idea why the render has this error?

Answer 1

The issue is your materials having a massive displacement:

The displacement scale is rarely above 1, in my personal experience it's even quite often in the decimal ranges, like 0.1.

Not only this, but most of your displacement maps in your whole scene are just flat, so completely useless:

By plugging these in, they effectively uniformly displace your whole geometry by the difference of the texture's value and your Displacement Node's Midlevel value. But if you have flat displacement maps, you shouldn't even use them, at best it's a waste of resources, at worse they make unwanted deformation like we have here.

To do this, select the materials that have them, such as perete-alb, and delete the image texture node and the displacement node.

You might also want to report these faulty materials to Poliigon since they are effectively sending you bad data.

Secondly, even for the materials that do have valid displacement maps, you want to make sure that the displacement scale isn't too strong enough, and If you want real geometry displacement: make sure there is enough geometry to displace in the first place.

Example with Trvertin:

I enabled the wireframe overlay to highlight the issue. Since your geometry is essentially just a big empty plane, and the displacement so strong, then the very few vertices are drastically moved, and the end result is terrible.

If you do not need real displacement, you could simply change the material's displacement property to Bump Only.

This will limit the displacement to being just a fake one on the shader level. It's the most cost-effective solution. And if you don't make close up renders where we can clearly see the silhouette of the geometry, it won't even make a noticeable difference.

But if you need to see the geometry being deformed, then either use Cycles, to use your material's Displacement (with or without bump), and Cycles's adaptive subdivision to quickly subdivide your mesh evenly.
Or if you want to use Eevee, you won't have adaptive subdivision, so you will need to manually adapt the geometry to have an even and high-enough mesh density for the displacement texture to look good.

To show you how it's done with Cycles, in the render properties, switch the feature set to experimental. Which will allow you to use adaptive subdivision.

Select one of the object with that material, press ⇧ ShiftL > Select Linked Material, and press ⎈ Ctrl2 to add a subdivision modifier to the selected objects.

Next, we need to change the subdivision settings for all selected object. Any time you click a property, hold down ⎇ Alt to propagate the change to the whole selection.

So while holding down ⎇ Alt, set the algorithm to Simple, and enable Adaptive Subdivision:

You might notice the message at the bottom of the modifier, informing you that your GPU isn't being used for subdivision. If you have a powerful GPU, it's worth fixing that issue:

1. ↹ Tab in edit mode, select all with A, open the edge menu with ⎈ CtrlE and hit Clear Sharp.
2. In the mesh data properties > Geometry Data panel, hit Clear Custom Split Normal Data

Then all you have to do is switch your viewport shading mode to rendered, and tweak the material's displacement scale:

As you can see, it needs to be quite low. Note that adaptive subdivision is particular: it adapts the subdivision with a relation of each (batch of) pixel and relative distance of the mesh, but it only shows when rendering, and it only updates when running a new render. So when previewing in the viewport, to update the subdivision after moving your view, you need to get out of rendered shading and back again.

If you notice some meshes that look stretched or diagonally distorted, it's usually either because they are triangulated or their geometry too uneven to handle, even with adaptive sampling.
This is also the inevitable required step to take if you want to use Eevee and its regular subdivision modifier.

With all its mesh selected in edit mode, open the face menu with ⎈ CtrlF and hit Tris To Quads to get rid of the triangles. If the geometry is too uneven (like those pillars at the entrance), use ⎈ CtrlR to add more edge loops and make the rectangular faces be closer to squares.