I’m having a serious rendering issue with a large architectural visualization scene in V-Ray for SketchUp and I’m trying to understand what’s causing it.
A few days ago, this exact scene was rendering in roughly 2–5 hours per image. Since making some modifications, render times have become completely unreasonable.
The main changes were:
Changing the Sun position/settings.
Modifying the water material.
Adding some vegetation and scatter elements (although nothing extreme).
At first, I thought it was just a heavier scene, but I launched a render at midnight and it was still rendering the next morning. I let it continue as a test, and after almost 48 hours it still wasn’t finished.
What makes me suspicious is that I noticed the render slows down dramatically around the reflections of the sun on the water surface. It looks like the renderer is spending an enormous amount of time resolving noise in those bright reflective areas.
Scene information:
V-Ray for SketchUp
Exterior scene
Water surface with reflections
Previously rendered correctly in a few hours
Has anyone experienced something similar?
Could this be caused by:
Caustics?
Reflection/refraction depth?
Sun angle creating difficult light paths?
Something else entirely?
I’ve attached an image of the scene and would appreciate any advice on where to start troubleshooting.
if you’ve got caustics turned on I would probably say that is to blame.
But maybe that’s just scratching the surface - if you can share the file I’m happy to take a closer look.
Also, if you’ve turned the noise threshold to a number too small; it will literally not stop as it will keep waiting for new photons to hit the pixel - on a very low lit screen like this that is quite plausible - especially with caustics turned on.
Thanks everyone for the suggestions. I finally found the issue.
The water material had its Refraction set to 100%, which was causing V-Ray to spend a huge amount of time calculating light transport through the water surface. Since the scene contains a large body of water and a low-angle sun, the render became extremely expensive.
Out of curiosity, I set the Refraction to 0% and ran a test render. Visually, there was almost no noticeable difference in the final image, but the render time dropped dramatically.
After disabling refraction, I was able to render the scene at 4000 × 2250 px, with V-Ray Quality set to High, and the render completed in a reasonable amount of time of 7 hours which is ok i guess ?
So in my case, the bottleneck was not the geometry, vegetation, or resolution, but the fully refractive water material. The visual gain was negligible, while the performance cost was enormous.
The only parameter that changes really for an transparent material - water or glass is the IOR which will be between 1.33 and 1.9 at the most extremes. I don’t think this would change the render time much as it basically represents and angle.
If you are ever in doubt with a material - the “presets” button is great , as it will create a simple material for you
