Invisible to camera, yet still renders

[Justin Hunt]

I have a problem

 

When obects are set to be invisible to the camera, they still render when an opacity mapped object overlaps or is in front of it, ie I am looking through

the transparant object I can still see the invisile object, outside the transparant object renders correctly.

 

In the tree example, the trees with red trunks are 3D Foliage objects that

are set not to be seen by the camera and the real looking trees are Plane

obects with a opacity mapped tree bitmap. The 3D trees are rendered within

the 2D planes and invisible outside the planes.

 

In the Glass roof example, there is a cylender surronding the scene with a

Cityscape mapped onto it and set to be invisible to camera, yet it is

visible through the glass roof.

 

How do I get these to work? I am rendering with MentalRay

 

JHV

[abicalho]

You need to make them invisible to reflections. That will stop them from rendering. Opacity Maps are reflections/refractions with no Index of Refraction from the renderer's point of view.

[Justin Hunt]

Isn't that a little pointless, the whole reason for the cylender being there is for the reflections.

[nisus]

Visible to camera is not the same as visible to reflections ,-)

Turn both off

 

nisus

[Justin Hunt]

You are completly missing the point. I want the reflections but I dont want to see the object anywhere else. Not in the backround, not through transparent objects ONLY in the reflections.

 

It is possible with scanline, just not Mentalray.

 

JHV

[nisus]

Hi Justin,

 

So basicly, you only uncheck the 'visible to camera'. And at this time your problem occurs. But why do you have 3d-trees behind Xtrees?

 

What RTdepth are you using? Turn that up?

 

rgds,

 

nisus

[Justin Hunt]

The "visible trees is just an image mapped onto a plane facing the camera. Due to the angle of the sun to the camera and trees these would only cast a thin shadow. To get proper shadows I used the 3D trees. The 3D trees look ugly but cast nice shadows. This is just one application, there are others

 

These examples explain the issue better

 

JHV

[nisus]

Hi Justin,

 

The problem is because when you look through the opacity mapped plane, there is (still) a refraction with IOR 1. As you can see in your example with the knots, you will need to turn off visible to refl/refract too.

This off course will not make the objects show up in the reflection... (so I do get the problem)

 

The workaround could be like this:

- with a raytrace material, I think you can control refract and refrect seperately. This can help you imho.

- for the trees: use the MR facade-shader (although I cannot get it to work properly, so if you can, pls tell me!)

- do not opacity mpa, but use geometry

 

rgds,

 

nisus

[Justin Hunt]

I had thought of the Facade map, but havn't tried it yet, whats not working for you?

 

In the examples all the reflections are calculated with a Raytrace material, I'll check the refraction settings, Off the top of my head I think no refraction is being calculated.

 

Thanks for the suggestions, but I think that this is a bug that needs to be reported.

 

JHV