I'm sorry if I misunderstand what you meant, but are you saying that it took 3.5 or 4 hours each frame?? BTW I also understand that you use AA of 16?
If so, let me tell you: that, is an extremely high setup and render time. rarely I use AA 8 or higher. if you have noisy renders, there is something in the scene that cause it. maybe you forgot, or you ignore it, but there is many ways to optimize any scene in TG: for example check the atmos quality, if you are using fog, check there is an excessive setting or unnecessary like "recive shadows from surface" enable or "cloud quality" in 0.2, for example. GI settings can also very problematic. I dont know, just to keep it in mind for your next animation, assuming I understood correctly what you meant
yes that was per frame render time
And actually I can tell you it's not bad!
I ran many tests and spent lots of time finding the best compromise between quality and render time. I was running crop regions with different AA settings, detail and even lower resolution texture but it all came to the same result: fine details requires high AA. Atmo quality was set to 24, clouds to 0.3 and of course surfaces were not tracing shadows on the atmosphere or clouds.
But to be honnest it makes sense as most of the time is spent on the raytracing process of the objects. This was one of the things Terragen was a bit slow at that time, but with the implementation of the Embree core in TG4 it is much faster (thumbs up Matt!). Now I can have the same scene rendered in twice the time, or I can trace the objects shadows into both atmosphere and clouds at no additional cost (compared to TG3)
Considering that this was a 2K full cg environment with displacement, billions of triangles plus the extra shading time, I find it to be pretty good. I am still waiting to see any other renderer rendering the same scene faster.
I know for sure that a scene like this rendered in Arnold for example would take at least the same time, if not (much) longer. And usually most of the time you don't have atmosphere or volumetric clouds as this comes as an extra pass and therefor extra render time. This would also be without the spectral lighting, which would also be quite expensive. However a brute force renderer like Arnold would probably give much nicer GI.
Speaking of GI, I could have had a better GI solution I think as interpolating 5-frames caches was adding a solid 15-20min per frame which seemed a bit heavy. But I was to lazy to run too many tests on it that so I just let it run. The indirect illumination in this scene is not really important anyway.
But I can assure you that 3.5-5h per frame is quite standard in the vfx industry. I've seen and continue to see much (much MUCH) higher render times at work!