dodgy reflections

V-Ray for Maya V-Ray for Maya :: Issues
1

Hi All,

I seem to have a re occurring issue when rendering cars with supplied Cad data. I don’t do too many cars so sorry of this is a ‘noob’ question.

Anyway it seems that my reflections don’t take into account normal smoothing on the supplied geometry and they become faceted and follow the tessellated shapes. It there a work around or am i too just retouch this out in post. See screengrab below,

Thanks

Matt

Capture.JPG
Capture.JPG750×847 74.7 KB

2

Reflections should take into account the normal smoothing.
Can you show us how the reflections look like when the edges are not smoothed?

3

Hello,

thanks for your response, here are the images requested

Reflection on supplied CAD by client below

Unlocked normal and set to hard edge

Set normal angle 30 degrees

It looks like there is some smoothing, maybe its the way it has been converted from nurbs. Exactly the same ting happened on the last job we did for another Japanese car manufacturer.

Let me know if you would like to look at a sample scene? and if so do you have an ftp i can upload to please.

thanks

Matt

supplied cad smoothness.jpg
supplied cad smoothness.jpg1750×1900 86.3 KB

unlocked and normals set to hard edge.jpg
unlocked and normals set to hard edge.jpg1750×1900 93.9 KB

set normal angle 30 degrees.jpg
set normal angle 30 degrees.jpg1750×1900 88.2 KB

4

Yes, a sample scene would help.

5

hello,

Please find attached a sample scene. Let me know if you want anything else

thanks

Matt
sample_scene.zip (4.17 MB)

6

I’m not sure if it’s possible to get perfect reflections in this case, since even with smooth normals, the reflection rays will start from a flat surface. High quality subdivision can smooth the reflection, but judging by the resolution you are rendering, you will not like the render times… But I can’t think of another solution currently. Someone more experienced with this may know at least faster work-around.

7

Hi,

thanks for the reply, yeah there is a pre scale of 8 on my camera and offset so i can render 10% and get an idea of final res. i think the whole car is 10k across but that issue is still visible, also I cant subdivide as its a dirty nurbs conversion. Last time i remodelled body panels so i could subdivide more but i wont be going down that route again :slight_smile:

Let see if anyone else has any suggestions

thanks

Matt

8

I had this issue before and the high subdivision route worked well, if it is a 10k image I would render it with distributed rendering. Even if render time is increased, I think re-modeling the car it would take longer.

9

you can’t touch the normals from cad. The way they have them there its set for special crease edges only, so if you just simply unlock and set normal smoothing on everything it wont work anymore. You need to export the normal data as is from cad.

10

Hi im not quite sure how i can subdivide as its not quads so doesnt smooth well, plus i dont have access to original nurbs surfaces to re tesselate.

11

Hi Dimitry. unfortunately i dont have access to the original nurbs cad.

thanks matt

12

OpenSubdiv realy fails on this data, but the V-Ray’s standard subdivision was not that bad (at least on that part you attached).

13

The very first picture you shared in this thread is the expected behavior for that kind of tesselation and image resolution. As Dimitri said, you can not touch the normals from CAD data, you have to take them as is. You would need the CAD data in a finer tesselation, but these need to be delivered from the client. If they cannot deliver finer tesselation, they have to live with that result.
Mostly we smooth out these reflections in post, but this only works for still images.

14

Hi Kosso,

thanks for your reply, i thought that would be the case just wanted to here if it was me or everyone else suffers the same issue. On this occasion an easy fix in photoshop.

Thanks

Matt