V-Ray reflection problems

[designimpressions]

Hi, I am trying to match CG objects to a background plate with 3DS Max & V-Ray using a HDR image for lighting & reflections. I want the CG objects to both reflect the environment and the surface they sit on. I created a plane object and assigned a vraymtlwrapper with the Background image as the base material.

 

The problem is that the CG objects appear to be transparent rather than reflecting the surface/ground. Is it possible for the cg objects to reflect the ground rather than appearing transparent and seeing through them to the background. It appears that the objects are just reflecting the background as an environment rather than a ground plate. I hope this is clear. I have attache an image showing you what I am tring to achieve.

 

Please see the attached images:

 

1, IBL with matte shadow.jpg showing the problem reflections

2, Environ. & Material settings.JPG

3, IBL Teapot.jpg showing an example of what I am trying to achieve. This was done with mental ray shaders.

 

Any help is much appreciated.

 

Thanks,

 

Peter

[Sketchrender]

did you look up peter guthrie

his tutorials are great.

[designimpressions]

Thanks Philip, I will check his site now.

[Guest ronalle]

you can try doing this using the matte shadow properties in the vray object properties dialog if the material wrapper is giving you problems....select the object you want to use as the matte -right-click and select vray object properties...matte properties you can set alpha dist, to -1 to have the matte appear in the alpha channel...... tip. dont store lights with irradiance map in the vray light properties, check out http://www.spot3d.com hope this helps.

[designimpressions]

Thanks for your reply Ronalle. I tried tried creating a matte from the plane using the vray object properties, the problem with this method is that it's not possible to add a base material which I need a cg object to reflect. It seems there is some sort of reflection using the VrayMtlWrapper but it's not to scale, it should be 1-1. Perhaps it's a limitation of V-Ray, CG objects can't reflect a VrayMtlWrapper Base Material properly.

[Guest ronalle]

hmmm....what about...dont use vraymtlwrapper at all. i thought of two methods... for the effect...

1.create the ground material and apply it to the plane...use the vray properties to create the matte....i think the material on the matte object would still be visible in reflections.

2. create two planes....one for the matte and one for the material you want to reflect...use invisible to camera on the later...it would still be seen in reflections.

hope you understand...am not too good at explaining.

[designimpressions]

Thanks again Ronalle, your explanation is perfectly clear. I actually tried applying the background map to a plane last night and the reflections didn't look natural because the image on the plane didn't line up with the background and the CG objects where reflecting a different part of the background image due to the different perspectives. I'll try again with a second plane mapped with the image and invisible to the camera, it's difficult to match the image mapped on the plane to the background image but I'll give it another go. Pity V-Ray doesn't have a Shader similar to mental ray's Environment/Background Switcher which allows a separate Background and Reflection map. Cheers Peter

[designimpressions]

...just an update. Basically the image assigned to the matte planes isn't orienting or scaling to match the background and the reflections are blown up. If I assign a uvw map modifer to the plane the image simply aligns to the plane as you would expect and doesn't match the background and the reflections are out of sync.

 

Please see attached images:

 

1, the matte is deactivated and the plane displays the background blown up and the reflections in the CG objects

2, the matte is activated and the reflections are just showing in the CG objects

3, the composition with the reflection mis=match with the background

 

Thanks,

 

Peter

[Stephen Thomas]

Just in case you get an email saying I replied to this, I misread the question and didn't realise you were using an HDR for reflections so I deleted my post!

 

Although can you tell me if you are also using a single photo as a background image, or is it just the HDR? If so, my initial idea might still apply...

[designimpressions]

Hi Stephen, I am using a single HRD for the lighting and reflections but the background is a sequence. Cheers Peter