Consider the following setup:

- a camera
- an object in front of the camera
- a solid/non-transparant wall behind the object
- a light_source behind the wall

Now, for some arcane reason, I want the light_source to shine on the 
object while the wall remains visible to the camera.

I first thought of a light_group {} with object and light_source in it, 
but the wall still blocks the light.

Any smart idea? I am sure it should be possible and I have the nagging 
feeling that it has been done before.

-- 
Thomas

Post a reply to this message

Am 08.11.2017 um 13:36 schrieb Thomas de Groot:
> Consider the following setup:
> 
> - a camera
> - an object in front of the camera
> - a solid/non-transparant wall behind the object
> - a light_source behind the wall
> 
> Now, for some arcane reason, I want the light_source to shine on the
> object while the wall remains visible to the camera.
> 
> I first thought of a light_group {} with object and light_source in it,
> but the wall still blocks the light.
> 
> Any smart idea? I am sure it should be possible and I have the nagging
> feeling that it has been done before.

Did you try no_<https://youtu.be/_euDhMDDRq4>?

Post a reply to this message

On 11/08/2017 07:36 AM, Thomas de Groot wrote:
> Consider the following setup:
> 
> - a camera
> - an object in front of the camera
> - a solid/non-transparant wall behind the object
> - a light_source behind the wall
> 
> Now, for some arcane reason, I want the light_source to shine on the 
> object while the wall remains visible to the camera.
> 
> I first thought of a light_group {} with object and light_source in it, 
> but the wall still blocks the light.
> 
> Any smart idea? I am sure it should be possible and I have the nagging 
> feeling that it has been done before.
> 
Have you tried the no_shadow object qualifier on your wall object?

If no_shadow cannot be used for some reason, perhaps the light_source's 
'projected_through' object feature might do the trick? There the object 
could be a say thin box of sized how ever you want relative to the wall 
and toward the object(1) from the wall. To this object you'd add the 
usual no_image, no_shadow, no_reflection qualifiers as needed.

Bill P.

(1) - An idea I've had on my to to-try list for a long while, is to 
variously light all the rooms in a large building - or a bunch of street 
lights say - with a single light source using the projected_through 
feature with a multi-shape object providing for 'magic light wormholes' 
into each room/location. Think it would work to the first order. Unsure 
it would result in a faster render - and perhaps the look of the lights 
would be too limited...

Post a reply to this message

On 11/08/2017 08:21 AM, clipka wrote:
> Am 08.11.2017 um 13:36 schrieb Thomas de Groot:
> 
> Did you try no_<https://youtu.be/_euDhMDDRq4>?
> 

:-)

Post a reply to this message

Le 17-11-08 à 08:27, William F Pokorny a écrit :
> On 11/08/2017 07:36 AM, Thomas de Groot wrote:
>> Consider the following setup:
>>
>> - a camera
>> - an object in front of the camera
>> - a solid/non-transparant wall behind the object
>> - a light_source behind the wall
>>
>> Now, for some arcane reason, I want the light_source to shine on the 
>> object while the wall remains visible to the camera.
>>
>> I first thought of a light_group {} with object and light_source in 
>> it, but the wall still blocks the light.
>>
>> Any smart idea? I am sure it should be possible and I have the nagging 
>> feeling that it has been done before.
>>
> Have you tried the no_shadow object qualifier on your wall object?
> 
> If no_shadow cannot be used for some reason, perhaps the light_source's 
> 'projected_through' object feature might do the trick? There the object 
> could be a say thin box of sized how ever you want relative to the wall 
> and toward the object(1) from the wall. To this object you'd add the 
> usual no_image, no_shadow, no_reflection qualifiers as needed.
> 
> Bill P.
> 

The object in a projected_through is NEVER visible. It never cast 
shadow, is never seen in reflections nor refractions, and don't affect 
radiosity. Ity's just a kind or portail through the light comes.

Post a reply to this message

>
> I first thought of a light_group {} with object and light_source in it,
> but the wall still blocks the light.

You almost had it: Light_group of object and light_source, ALONG WITH no_shadow
for the wall.

Here's a small test scene, with two cameras to test that it works, and an extra
front-light to show that the sphere object still casts its own shadow on the
wall.
------------
#version 3.71;
global_settings{assumed_gamma 1.0 max_trace_level 5}

camera {
  perspective
  location  <.5, .5, -5>
  look_at   <.5, .5,  0>
  right     x*image_width/image_height
  angle 67
}

/*
camera {
  perspective
  location  <30, 30, -5>
  look_at   <.5, .5,  0>
  right     x*image_width/image_height
  angle 80
}
*/

// wall behind object
box{0,1
no_shadow
translate <-.5,-.5,0>
scale 30*<1,1,.1>
pigment{rgb .7}
translate 1.5*z
}

light_group{
light_source {
  0*x
  color rgb <1,1,1>
  looks_like{sphere{0,1 pigment{srgb <1,.5,0>}finish{emission 1}}}
  translate <-15, 15, 20>
}

// object
sphere{0,1
pigment{rgb <0,1,0>}finish{ambient .05 emission 0 diffuse .8}
}
}

// extra DIRECTION POINTER between light and object
cylinder{<-15, 15, 20>,<0,0,0> .1
no_shadow
pigment{rgb <0,.5,1>}finish{emission 1}
}

// extra front-light for object and wall
light_source {
  0*x
  color rgb .4
  translate <20, 5, -20>
}

Post a reply to this message

clipka <ano### [at] anonymousorg> wrote:

>
> Did you try no_<https://youtu.be/_euDhMDDRq4>?

That video is blocked in the U.S. :-(  It probably contains confidential State
Secrets...

Post a reply to this message

"Kenneth" <kdw### [at] gmailcom> wrote:

>
> You almost had it: Light_group of object and light_source, ALONG WITH
> no_shadow for the wall.
>

Hmm, for your real scene, I think there is still a problem: How to get your wall
to cast its own shadows from other lights in the scene. With my test set-up, it
doesn't do that, as the wall is necessarily made no_shadow in order to work
correctly :-/

I tried adding an identical NO_IMAGE wall into the light_group (without the
no_shadow tag), but that doesn't work-- this extra wall again blocks the light
to the sphere object.

My past use of this set-up never needed the 'wall object' to cast its own shadow
(I was shining a light up through a no_shadow height_field.) I wish I could
suggest a workable solution...

Post a reply to this message

On 8-11-2017 14:21, clipka wrote:
> Did you try no_<https://youtu.be/_euDhMDDRq4>?
> 

I did. Got a bit bruised... :-)

Good music by the way, but I had expected more from the POV-Ray scene 
render and the use of Poser figures. I missed the chequered plane...

-- 
Thomas

Post a reply to this message

On 8-11-2017 14:27, William F Pokorny wrote:
> Have you tried the no_shadow object qualifier on your wall object?
> 

Incredible! Just adding no_shadow does the trick indeed and exactly as I 
need it, without the light_group even. I had not thought of this at all 
as the name implies that the object does not cast shadows, not that it 
also becomes transparent to the light. This is not implied in the docs.

Thanks a lot!

> If no_shadow cannot be used for some reason, perhaps the light_source's 
> 'projected_through' object feature might do the trick? There the object 
> could be a say thin box of sized how ever you want relative to the wall 
> and toward the object(1) from the wall. To this object you'd add the 
> usual no_image, no_shadow, no_reflection qualifiers as needed.
> 
> Bill P.
> 
> (1) - An idea I've had on my to to-try list for a long while, is to 
> variously light all the rooms in a large building - or a bunch of street 
> lights say - with a single light source using the projected_through 
> feature with a multi-shape object providing for 'magic light wormholes' 
> into each room/location. Think it would work to the first order. Unsure 
> it would result in a faster render - and perhaps the look of the lights 
> would be too limited...

That would be a very interesting thing to do indeed.

-- 
Thomas

Post a reply to this message