glass + hdri against background

[sniikki]

Sorry to ask this again since I found several threads about this but none of them had answer.
Many has had this problem with all versions of vray.

So first, images says more than thousand words



In first pic there's car glasses against background pic (set to max's environment) and scene has hdri of same place set to vray's reflection/refraction slot.
You can't see the background through the glass coz they refract the hdri in some weird way. Everything inside the car shows up fine through glass.

Second pic is taken from inside the car and background is set white from max environment but, well you can see how it looks.

Glass material is done normally (like everyone else does it) and I tried egzGlass too with no luck.

So what causes this weird bug and is there anyway to solve it?
I'd like to composite the car into background image but it's impossible coz of this and it doesn't help if i use empty background and with alphachannels do the compositing afterwards coz those weird glass bugs get in alphachannels too.

Here's the whole car rendered with ground and background planes (so no empty background can be seen through glass) and it works fine.

http://users.evtek.fi/~anttimak/s3/audi38.jpg

[percydaman]

lower your glass's IOR alot. try 1.2

[Dynedain]

Make sure your glass object actually has a thickness.

[percydaman]

that too...lol

[sniikki]

It has thickness (shell modifier and also tried with just a thin box)

And I also have tried with IOR 1.00 etc.

[Da_elf]

for my cars i usually use ior 1.001

[percydaman]

what version of vray are you using? if its not vray free, you need to email chaos and get access to the licensed user section of the forum. This section of the forum is for the public demo.

[sniikki]

I have just the free version at home. In school it was 1.46 or 1.47 , don't remember.

[Sushidelic]

As the HDRI map overrides reflection AND refraction, it is absolutely normal that you see this map through your windows, as they are refracting. You can come across this issue by placing an image plane with your BG map at 100% selfillum aligned to the camera far in the back of your scene, set it to invisible to camera and voilà!

Regards, Michael

EDIT: Ooops, just read your post to the end... Looks like you already discovered the solution. BTW, a screen mapped BG seen through glass would cause refraction weirdness anyway!

[sniikki]

Hi sushidelic,

Thanks for tips.
But why whould I place bg plane there and then set it invisible? For refraction? Wouldnt it be quite hard to get the plane matching the picture where the car will be composited? (so that the plane would be in same size, place and angle than the actual bg pic)

[charbroil]

I'm having the same problem and I'm using advanced. I have a gradient (which is actually a bitmap) for the max environment. It looks good except for where it is behind glass. When behind glass, it reflects nicely, but looks almost black and you can't see the gradient. Also, other modelled parts of the scene look totally fine through the glass, it is only the background that doesn't. I have tried every setting I can think of, with no luck. Is this the same issue?
Thanks.

[Sushidelic]

@sniiki: sure you don't have to set the plane invisible to camera if you take things straight out of the renderer, but you'll probably miss an alpha afterwards. And usually it's fairly easy to match the BG plane close enough to your Max BG.

@charbroil: Do you use different environments for Vray and Max? Did you probably override the Max BG with a black one in the Vray render settings?

Regards,
Michael

[charbroil]

You are totally right. I changed that a while ago when I was testing something and never changed it back...of course. Thanks.

[sniikki]

charbroil,
yes u had same issue, but in my case, i want to have hdri reflections with different bg or empty bg.

Isn't there any way to for example put a plane behind the car and make that plane not to cast reflections and not affect the alpha?
Meaning that it would show up in back as a white bg but wouldn't reflect to car. That way (coz if there's object that can be seen through the glass I won't get those hdri refractions for glass) I could get the car nicely composited to another picture and other side of the glasses would be clear in alphamap.

Hard to explain, hope you understand