How to have transparent (invisible) material

[Bogdan_Brezden]

Hi, I’m trying to make a transparent / invisible material that would also cast shadows. This so that I could reveal how, throughout the day time, light penetrates the windows. In order for this to happen, I need to make the wall and the polls cast shadow into the interior part of the building, but in the same time I also need the wall to be transparent so that the interior would be visible for people to see how light functions within the building.
I used glass material but that didn’t give me any shadows, I tried to make V-Ray material that would be transparent similar to that of Christopher McAdams [Advanced Materials] Part 3 - Adding Invisible Materials video. So far, I was able to make a reverse formula that would make the material similar to glass but it doesn’t make shadows. Is there any way to make a transparent material that would give me shadows or make the material invisible but still react to light?

[Tom_P]

there was a topic within the last weeks about how to render shadows only, not the object … i can t find it … sorry.

but there is similar questions.
maybe closest:

Transparent but still cast shadows?

I am trying to create a “ceiling” in a room that is transparent for the purposes of modeling and viewing the room but still is opaque to lights, sun etc. I’ve tried to get a transparent surface to work and monkeyed around with a horizontal clipping plane below an opaque surface but neiter approach seems to work. Seems like this ability would be useful for people modeling interior spaces who want to see the effect of windows etc. Any advice? Nick

also here with less answers

similar topics i ve found:

Rendering Shadows of Hidden Objects onto Visible Objects

Basically here is what I’m trying to achieve: I’d like to get a rendered elevation view of a particular wall WITH the shadows of the object next to it (behind the camera). I only want to see the shadows the object is casting, so I can get an outline in parallel elevation view of the shadow cast on a neighbouring wall. I’ve tried to use a ClippingPlane but as soon as the shadow-casting object disappears from view, so does the shadow it casts. I’ve also tried OrientCameraToSrf but the shaows ar…

Rendering shadows without the object being there?

This is how currently Raytraced/Cycles works in Rhino WIP. Room lit by sun through circular opening. Wall near orange cube is reflective (with slightest hint of roughness). Green pyramid is behind the clipping plane (i.e. clipped), but still shows in the mirror wall. No lighting happening through the clipped side. [kuva]

[Bogdan_Brezden]

Hey Tom, thank you for replying, unfortunately I have done a lot what others have suggested on their forums and it doesn’t seem to do the job. I am still not seeing the shadows of the wall, is there a method with V-Ray format to get the wall invisible since I’ve been seeing people were talking about that more often?

[Gijs (Gijs de Zwart)]

Did you try the clipping objects? It’s been a while that I used them but I think it should allow you to clip geometry for camera rays only. In Vray’s courseware there are some examples of object based clipping

[Micha]

Right, a clipping plane should help to solve the situation. In the past I used a clipping plane and placed it so that the whole scene was clipped but switched the Exclusion mode from exclude to include. So, you can define objects per “pick” which should be hidden.

[Bogdan_Brezden]

Thank you for replying, unfortunately many of the method including clipping plane, transparency option for material, CP, and V-Ray format didn’t work for me, there seems to be an in issue when I change the material to be transparent or when I do other commands, the shadows don’t appear at all. In fact, I tried with experiments to make it visible again, and it becomes partially visible or fully it still won’t give out any shadow. What could result in such thing?

[Gijs (Gijs de Zwart)]

I think the attached sample is what your approach should be. The object in front is set to be clipping geometry and the Clipper object is set to not affect light in the options.
clip_sample.3dm (450.9 KB)