Best way to optimise large terrain scenes?

[Sulphurous]

So I've noticed that for whatever reason when i render a scene that has large background objects renders seem to take 10x longer than they would normally. Even if i have as little objects as possible in view, this still occurs. What's the cause of this? https://prnt.sc/ileyoo The scene i'm creating in question.

[maru]

That's interesting. Can you send us any scene where this can be observed? https://corona-renderer.com/upload

[Sulphurous]

Some extra information i should have mentioned, here's all the active objects i have in the scene. http://prntscr.com/ilfxxx
If i disable almost everything the render proceeds very quickly, however the part i'm talking about in particular is the de-noising process. I have the GI/AA balance set to 24, and Light Samples at 4. I used to have light samples at 6, and tried out 32 GI/AA balance, not sure how much render time that will affect. Also, i've boosted up the denoising amount to 0.90 from 0.65, though i'm not sure if this option even does anything as i have full denoising enabled anyway. UHD cache is set to animation (flicker-free). Pass limit is 10, noise limit is 3. If this is an issue with my system and not the settings, it would be good for me to know in order to achieve an efficient workflow. http://prntscr.com/ilfzze The passes is what takes <80% of the render time.

[TomG]

I notice in your screenshot that your memory is pretty much maxed out - this will cause significant reduction in render speed. Looks like there is a lot of geometry here with the landscape objects, so that could be what is pushing the memory up so high, and would likely result in slowdowns (and why the slowdowns show up depending on the objects you add).

Other notes

- Denoising amount always has an effect, it's the amount of blending between the un-denoised version of the image and the denoised version, and applies whether Denoising is set to Full or Fireflies only. See https://help.c4d.corona-renderer.com/support/solutions/articles/12000021554-how-to-use-denoising-c4d-

- Denoising won't significantly affect render time. It may affect memory requirements though, especially depending on image resolution (the larger the image, the more memory required), and passes in MultiPass (the more passes that have Denoising applied, the more memory required). Depending on your scene (would still be good if you could send the scene as Marcin requested :) ) there could be memory savings to be found here, e.g. lower resolution, less multipasses, etc.

- With a pass limit of 10 and noise limit of 3, it is most likely stopping at the pass limit of 10 (usually it would take more than 10 passes to get down to a noise level of 3%). Remember that the renderer stops whenever any ONE of the limits is reached (time, passes or noise level). Helpdesk articles like https://help.c4d.corona-renderer.com/support/solutions/articles/5000518064-how-many-passes-is-enough- explore things like passes, GI vs AA balance, etc.

But, I think memory is most likely the issue in this instance looking at the screen grab.

[Sulphurous]

I notice in your screenshot that your memory is pretty much maxed out - this will cause significant reduction in render speed. Looks like there is a lot of geometry here with the landscape objects, so that could be what is pushing the memory up so high, and would likely result in slowdowns (and why the slowdowns show up depending on the objects you add).

Yeah i forgot to mention that was because i was rendering something, as shown in the second picture. Chrome seems to be the main culprit here. http://prntscr.com/ilguwa I like to have a few dozen chrome tabs open when im multitasking given i have enough memory, though it seems to be having it's own side effects. I'll get back to you on the other notes when i try stuff with more memory available.

Also, i'd very much like to provide full insight into what i'm doing by sending the scene, i'm just a little unsure of these things as i value the work i create. I'll definitely come up with something!

[TomG]

Scenes can be sent via the private uploader, then only the Corona team gets them and only for testing purposes :)

https://corona-renderer.com/upload

[Sulphurous]

I just noticed that i had ambient occlusion enabled as part of the render options, would that change anything?

[TomG]

A Corona AO in multipass? Or some native C4D AO? Not sure if the second works (I never use it :) )

[Sulphurous]

Native C4D.

[TomG]

I have no idea how much native C4D might add to memory requirements (I am still pretty sure it is memory that is the issue here). You could remove it and see what impact it has on memory use / render times.

In terms of memory use, another big source of memory requirements is displacement, so that might be worth looking at too if you are aiming to optimize the scene some.

[Sulphurous]

I've seen to run into a bit of a hiccup. The total file size of the scene is at 1.32 GB. Could large file sizes for scenes explain large render times? I've also added new items to the scene (self illuminated lights) and the rendertime has gone up to about ~15-21 minutes on average. I've also increased in the GI/AA balance recently to 64 (had 24-32 before) due to increased noise in the renders from the light. Not sure how much that will affect in 11 passes.

[Jpjapers]

I too have noticed significant slowdown in various render stages when chrome is open and i assume its because chrome is such a memory hog.

[Sulphurous]

I think i might have figured out the reason (not sure for certain as i'm still rendering), being that because i'm rendering in .TIFF file format at 32bit/channel gives me the same effect as rendering with .avi (slow, and a huge file size with no difference than PNG), i'm going to therefore try to use .png to render now. I'm planning to use mp4 to render animations so who knows.

[TomG]

One thing - for animations, always render to still frames, and composite to an animated format (mp4 etc) later. There are many reasons for this, the main one being that with most movie formats, if the render fails at any point, all work is lost. If you are rendering to still frames, only the current frame is lost and you can start re-rendering from that point onward.

This thread also makes me wonder how much of the animated format is held in memory or disk cache during rendering, since the whole file has to be built at once and can't be added to incrementally. Either way, definitely rendering to stills and composite into movie format later is a critical workflow for many reasons and may help with this issue too.

[TomG]

Other advantage (in case you really need convincing :) - with still frames, you can always experiment with different video compression settings, but if rendering to a video format the compression is baked in and you'd need to re-render to change it. And, if you've seen how long it can take to apply the codecs to stills when making a video format, bear in mind that rendering direct to video format is adding all that extra time into your render itself as well.