Problem with terrain subdivision and water.

[ndeewolfwood]

hi everyone,
i'm still working on a mountain lake scene in order to animate it.
You can see a short render here.
http://www.planetside.co.uk/forums/index.php?topic=14347.0

I have a problem with it and i need some help about it.
When my camera is very close from the water i've got a strange subdivision problem on the terrain under my lake level and only very close from the camera.
I've posted a picture where you can see  this problem. (right clic>open in new window for full resolution display)

I did some crop render without water in order to check this and offcourse the  problem disapear.

For water i'm using the water mask time saver tgc from Dandelo.(http://www.planetside.co.uk/forums/index.php?topic=8793.0)

My spec are :
size : 3000*1687
detail : .65
aa : 6
Raytrace object : on
GI : 2/4/1
Detail jittering is on for now (for this render) but i plan to turn it off when i will render animation.
Detail Blending :.5
Mircrovertex :on


Any idea ?
Thanks for help.

[Dune]

Someone had the same issue some time ago, and I think there's a remedy. Maybe search the forum or just wait for a person who knows...

[dandelO]

It's just the optimisation of water in the default renderer. Search the forum for 'render subdivision settings', once you insert that node into the renderer's internal network you'll have control over the subsurface render detail(ray detail multiplier).

[ndeewolfwood]

I've tryed values from .1 up too 100 for ray multiplier.

Globally it's working like expected but not in the picture bottom (the part closer from the camera) it always looks low poly.

Value over 100 do not look reasonable to me in term of render time (default value is .25 and slider go from 0 to 1).

The weird thing is the non progressive look of this.

Do you think i really need to explore values over 100 ?



 

[Oshyan]

Ray Detail Multiplier controls the multiplier for certain raytraced elements vs. the main scene detail. 0.25 is the default, meaning underwater geometry, reflections, etc. are rendered at 25% (1/4) main scene detail. A value of 1 means they should be rendered with equal detail to the main scene. So a value of 100 is... insane. If a value of 1 is not helping you, then there's something else wrong. I would never suggest using anything more than 2, and even that would be in extreme or unusual circumstances that I can't really think of right now (but probably there is some reasonable situation to do it, just not 100, hehe).

Anyway, it looks like it may be a bug. Can you possibly share the scene? You can send it to support AT planetside.co.uk. There may also be other settings in the Subdiv Settings Node that could help, though I'm not real familiar with those options yet. Something like unchecking "Fully adaptive", for example (just a guess).

- Oshyan

[ndeewolfwood]

Something like unchecking "Fully adaptive", for example (just a guess).

I've checked this just after reading what it does in one of previous post and it doesn't help.

Right now, i'm not on the right workstation to send you the file. I will post this directly here in few hours.

Thanks for you help.

[ndeewolfwood]

the file 
http://dl.dropbox.com/u/21114277/tibet_0004.tgd

[Oshyan]

Ok, so nothing really affects it except raising camera altitude a bit. You are very close to the water's surface and I suspect there are Level of Detail optimizations going on here that are causing problems in this specific scenario. It's probably something that could be improved, but the only solution I can see without back-end renderer changes is to increase camera height. I will open a bug report on this to track fixes in the renderer for the future (or perhaps Matt will know of a way to fix this with existing settings).

- Oshyan

[Oshyan]

Update: it appears I overlooked one relevant option. Setting Ray Detail Region Padding to 1 seems to fix the problem. Higher values may be required in some circumstances, but this seems to work on the camera perspective in the file you provided. I would guess this is due to the handling of refraction at the edge of the camera view.

Thanks to Kadri for this solution!

- Oshyan

[Dune]

I knew it was curable 

[ndeewolfwood]

cool nice find.Thanks Kadri, Oshyan,Dune and Dandelo.

I just want to double check.
If in use "Detail in Camera" for "Ray Detail region" and if i use ".2" for "Ray Detail region padding" it means : the raytracer will fully trace 20% more rays who are offscreen but who contribute to a in frame pixel ?

[Oshyan]

From a previous change log:

A value of 0 means no padding. A value of 1 adds a border to each side of the frustum which is equivalent to the width or height of the image or crop region, which makes the frustum 3 times as wide and 3 times as tall.

- Oshyan