Single sided material for reflections

[ryannelson]

Hey guys, I've tried to search through the forums to tackle this but I haven't come up with anything. Note: I'm using Vray 2.0 for Rhino 5.

 

What I would like to do is use a site photograph to generate reflections for a north-oriented shot (sun at viewers back). It is not a spherical HDRI where I can put it in the environment reflections slot, or in a dome light. It's a standard flat image. I thought I could create a plane infront of the building and apply 2-sided material and simply have one side completely transparent where the sun would pass through one side, and the glazing would pick up the image from the other side. Here is the result of my testing:

 

 

As you can see, the material still blocks the sunlight even though it's transparent.

 

Maybe this is a really simple thing that I'm making more complex than it needs to be?

 

I've tried doing this in post also, but I find that the reflections are never very convincing and they don't interact well with the reflections from the 3d environment. What do you do in this scenario?

 

Ideally, I would go to site myself and take a spherical panorama shot. I have done HDRI pano's in the past with my manfrotto pano head, but this is time consuming and often not warranted for a rendering.

[Chris MacDonald]

Tick "affect shadows" on the transparent material.

[RyderSK]

 

Maybe this is a really simple thing that I'm making more complex than it needs to be?

 

 

Yes. What you try to to is pretty outside of box, but suboptimal and not necessary.

While I don't use Rhino (and I did very long time ago in college, not enough to remember anything), it should have access to same Object/Vray properties (so not through material use), where you tick "affect reflections" only.

 

Alternatively, you can also paint alpha channel for your Sky, because flat jpeg image doesn't have enough dynamic range to create nice reflections (which happen because Sky is inherently much brighter than landscape). Then you don't need to mess with object properties, but simple regular VrayMTL with with alpha channel. Sky will become invisible, and your HDRi/VraySky will apply, and the landscape will reflect and also block lighting like it should. Alternatively the diffuse can be swapped with self-illumated slot.

 

Quick example on very old render of mine.

 

[ryannelson]

Thanks for the replies! Both are great tips, i'll give them a shot!

 

Juraj, I had actually thought to do that before but I was hoping for a "quick fix" with the 2-sided material rather than painting the alpha. Excellent work by the way, you're a master! I've been intending on migrating to 3dsmax too, but I still like to model in Rhino as well as use grasshopper. Time to learn yet another program too! haha

 

Cheers!

[RyderSK]

If you're lucky, some magic wand in PS might "quick-fix" it as well :- ) I just had weird overcast sky which proved harder to do automatically.