hello!

i am thinking about generating a synthetic ground-truth benchmark image for a 3d
scanner using povray. therefore i would like to know if and how it is possible
to simulate a video projector in povray.

it should be possible to simulate each projector pixel using a spotlight and
place a lens in front of the array, but that would be extremely tedious and
probably inaccurate.

is there a way to project a bitmap onto a scene, ideally with finite
depth-of-field? after all, a projector is just a reverse camera ...

thank you

Post a reply to this message

Christoph <nomail@nomail> wrote:
> is there a way to project a bitmap onto a scene, ideally with finite
> depth-of-field? after all, a projector is just a reverse camera ...

  Simply put the image onto a plane, apply filter 1 to it and put a
light source behind it. All the lighting from that light source on the
other side of the plane will be filtered by the image map, so it effectively
projects the image.

-- 
                                                          - Warp

Post a reply to this message

"Christoph" <nomail@nomail> wrote in message 
news:web.4905eeb55b9956825c2817dc0@news.povray.org...
> hello!
>
> i am thinking about generating a synthetic ground-truth benchmark image 
> for a 3d
> scanner using povray. therefore i would like to know if and how it is 
> possible
> to simulate a video projector in povray.
>
> it should be possible to simulate each projector pixel using a spotlight 
> and
> place a lens in front of the array, but that would be extremely tedious 
> and
> probably inaccurate.
>
> is there a way to project a bitmap onto a scene, ideally with finite
> depth-of-field? after all, a projector is just a reverse camera ...
>

Yes. You may find the following example helpful. It projects a bitmap onto 
the scene, which, in this case is just a plane.

The bitmap is projected by placing it in front of a light source and adding 
a filter filtering all of the colours in the image at their full intensity 
('filter all 1'). I'm not sure how you'd go about adding a depth of field.

Regards,
Chris B.

camera {location <-0.4,0.4,-1.4> look_at 0}
global_settings {ambient_light 0.05}

// Image to project
plane {z,-0.9
  pigment {
    image_map {
      sys "gear00.bmp"
      once
      filter all 1
    }
    scale 0.1
    translate -0.05
  }
}

// Projector
light_source {<0,0,-1>, rgb 1}
cone {<0,0,-1>,0,<0,0,-0.97>,0.02
  no_shadow
  texture {
    pigment {rgb <1,0,0>}
    finish {ambient 10}
  }
}

// Screen
box {<-0.5,-0.5,0>,<0.5,0.5,0.01> pigment {rgb 1}}

Post a reply to this message

> i am thinking about generating a synthetic ground-truth benchmark image for a 3d
> scanner using povray. therefore i would like to know if and how it is possible
> to simulate a video projector in povray.

If you want to simulate a real projector, you probably need to
model the lens. Of course, you can project the image just using
a point light source (basically an inverse pinhole camera model).
To get your image through the lens, you need to use photons (or
radiosity, but I think that would be painful to use here).

I once tried something like that, maybe it helps you get started:

http://news.povray.org/povray.general/attachment/%3C486aa74c@news.povray.org%3E/us-ascii

> is there a way to project a bitmap onto a scene, ideally with finite
> depth-of-field? after all, a projector is just a reverse camera ...

You should get depth-of-field when you model the lens.

Post a reply to this message

Christoph wrote:
> i am thinking about generating a synthetic ground-truth benchmark image
> for a 3d scanner using povray. therefore i would like to know if and how
> it is possible to simulate a video projector in povray.
> 
> it should be possible to simulate each projector pixel using a spotlight
> and place a lens in front of the array, but that would be extremely
> tedious and probably inaccurate.
> 
> is there a way to project a bitmap onto a scene, ideally with finite
> depth-of-field? after all, a projector is just a reverse camera ...

Depends on what you want. If you want it to look like a reallife projector,
you should probably use one of the suggestions you already got (using a
light and a texture acting as a filter).

If you really want a "reverse camera", use Rune's "illusion" include file:
http://runevision.com/3d/include/illusion.zip

Post a reply to this message

thank you very much, this looks promising!

Post a reply to this message