Shadow Catcher

[Jershaun 8]

Hi

How can I make an object in VW/RW invisible to the camera BUT still show the shadows cast on it?

Thanks,

[CipesDesign 76]

Hi Shaun, this sounds like a Zen riddle... Could you be a bit more specific as to what you're trying to accomplish??

[russh 0]

Shaun, do you mean you want an invisible object that still casts shadows, as you can in 3D studio? I don't understand how you can cast shadows on to an invisible object.

[Jershaun 8]

Hi Guys

What I want to do is place my 3D object (eg. signage pylon) against an existing photograph. I can just do this and leave it at that BUT to integrate the 3D object into the photograph it still needs to cast shadows on the "ground and walls of the photo". Thats the end result I would like to get. This could also apply to a building superimposed on a photo.

In C4D, I would do this: http://www.cineversity.com/tutorials/lesson.asp?tid=655

Thanks,

Edited February 7, 2008 by Shaun

[CipesDesign 76]

Easiest way I can think of would be to use the polygon tool to trace over the shadow(s) then delete (or make invisible via class?) the shadow producer. Of course this will only work for a static view... It will also require some trial & error with color(s) on the poly(s) for a realistic look...

[Benson Shaw 399]

You could try mapping a texture of the photo onto a 3d rectangle. Now the image is a 3d object which can receive shadows from other 3d objects.

I don't understand why the shadow casting object needs to be invisible. Seems like the bigger problem is making the shadows bend where photo shows surfaces on different planes, foreshortening, etc.

Shaun, post an example image and tell what is not working.

-B

[Jershaun 8]

Hi Benson

You're kind of right. In Cinema4D I would do exactly what you suggested, however C4D has a mapping type called "frontal" which will work because it wouldn't distort the background image in perspective. RW doesn't have a mapping type "frontal" so it would be extremely difficult to keep the background image flat yet still have a 3D polygon catching shadows. I'll see it I can create an image later.

Thanks,

[Jershaun 8]

Hi

If you look at the first attached image (888) (created in TC10-which is 4 years old), 2 cones, 2 spheres and 4 columns are casting shadows on a base which one can't see because it has a texture applied to it. The second image (889), one can see the make-up of the material.

VW, TC and ArchiCAD all use the Lightworks rendering engine and if one looks at image 3 (890), one can see ArchiCAD also has the "shadow catcher" reflectance. VW, which has a more recent version of lightworks than TC, still doesn't have this feature. Why not?

Thanks for looking.

[russh 0]

There's a lot of stuff in Lightworks that isn't in Renderworks. For no apparent reason.

I see what you mean now by shadow catcher. Excellent idea.

[Benson Shaw 399]

Hi, again, Shaun. That's what I thought you were trying to do. Your example does not show the shadows mapping up and over a curb or from ground to wall. Can the TC tool manage that?

I think you could get pretty close to this with VW by mapping the background image to a 3d plane. But it would likely be a painful, trial and error process getting everything oriented. It looks like TC's shadow catcher tool takes care of light angle and orienting the 3d objects to look like they are ground related.

I still do not understand the need for an invisible object which will cast shadows. Is there such an invisible object in your example? Do the 3d cones have a 2d contour which is sheared or manipulated to create the shadows?

Anyway, thanks for coming back with this.

-B

[Jershaun 8]

Hi Benson

As I said before the objects are lying on an extrude which the shadows are being cast on. This extrude has a texture applied to it which shows the shadows only but let's the background shows through. This creates the impression that the objects lies on ground/road.

Shadows can also be cast over walls or curbs in TC. All you have to do is put a vertical plane/extrude with the same texture applied to it.

Thanks,

[knickers 0]

Hey Shaun,

I know it's an old topic now, but did you ever find a way to achieve a Shadow Catcher in RenderWorks?

Nick

[Jershaun 8]

No.

Also I asked for this prior 2009 and from what I saw in the demo, 2009 doesn't have it either. I know Lightworks has the ability but for some reason Nemetschek hasn't included it in. TurboCAD (which uses lightworks too) had this feature since years ago.

[gScott 0]

benson,

in shaun's example image the grey road belongs

to the background image, there is no modelled

"floor" visible.

the shadows that are visible are being cast

onto the "shadow catcher", an invisible floor

in this case, and only the shadows become visible.

this allows for the model to cast shadows onto

a background without having to fake them in in

photoshop afterwards, or to fake out a floor that

they were being cast onto...

[cad@sggsa 0]

So why can't we do it in VW??...

Or rather Why have they not included it into VW???

If only there would be ONE program that could do it ALL

This sounds like our politics over here...1 major party and 10 other smaller ones competing againt one another to win the election.....they should just all stand together....