So, I'm doing a pigment layered by y-distance from the origin.  It looks 
great when I do the othagonal view from the positive Z and X directions, 
but when I render it from the positive Y direction, the object disapears 
from the render!  Why do it do that?

More importantly, how do I make it not do that?

-- 
Dawn McKnight                               d-m### [at] spamlesscoxnet
USS Nautilus cooperative writing project: 
                                    http://members.cox.net/uss_nautilus

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Dawn McKnight wrote:
> 
> So, I'm doing a pigment layered by y-distance from the origin.  It looks
> great when I do the othagonal view from the positive Z and X directions,
> but when I render it from the positive Y direction, the object disapears
> from the render!  Why do it do that?
> 
> More importantly, how do I make it not do that?

It would really help if you could provide a short example of the code
you are working with that would illustrate the problem and thus help
us isolate it for you.

-- 
Ken Tyler

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"Dawn McKnight" <d-m### [at] spamlesscoxnet> wrote in message
news:d-mcknight-9922A7.18395211022004@news.povray.org...
> So, I'm doing a pigment layered by y-distance from the origin.  It looks
> great when I do the othagonal view from the positive Z and X directions,
> but when I render it from the positive Y direction, the object disapears
> from the render!  Why do it do that?
>
> More importantly, how do I make it not do that?
>

Well, it's not a bug - orthographic cameras will do that unless set up
correctly. Best post an example scene and then someone who feels comfortable
with orthographic will be able to explain what's happening.

The section of the docs that relates to this are the last two paragraphs of
section 6.4.2.2

"You should be aware though that the visible parts of the scene change when
switching from perspective to orthographic view. As long as all objects of
interest are near the look_at point they'll be still visible if the orthographic
camera is used. Objects farther away may get out of view while nearer objects
will stay in view.
If objects are too close to the camera location they may disappear. Too close
here means, behind the orthographic camera projection plane (the plane that goes
through the look_at point)."

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"Tom Melly" <tom### [at] tomandlucouk> wrote in message
news:402b54a0@news.povray.org...
> "Dawn McKnight" <d-m### [at] spamlesscoxnet> wrote in message
> news:d-mcknight-9922A7.18395211022004@news.povray.org...
> > So, I'm doing a pigment layered by y-distance from the origin.  It looks
> > great when I do the othagonal view from the positive Z and X directions,
> > but when I render it from the positive Y direction, the object disapears
> > from the render!  Why do it do that?
> >
> > More importantly, how do I make it not do that?
> >
> Well, it's not a bug - orthographic cameras will do that unless set up
> correctly. Best post an example scene and then someone who feels
comfortable
> with orthographic will be able to explain what's happening.

Just for gits and shiggles, try adding this to your camera:

camera
{
    orthographic
    location <0, 0, 0> // or wherever.

    up y
    right image_width / image_height * x
}

The  last two lines always ensure that your picture doesn't get "stretched".
So circles are circles, boxes are boxes, etc. (technical term is aspect
ratio: if you have an image that is 400 x 300 pixels, the width (x) is
1+1.333 times the height, so your aspect ratio would be 1.333:1 -- plug
1.333 into "right" and tell POV-Ray which axis is "up" (y) and it make sure
that your objects are rendered with an aspect ratio of 1::1 regardless of
the aspect ratio of the image).

If I have some terminology wrong on here, somebody correct me please. I
don't speak well.

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In article <402AF54C.508F9AE8@pacbell.net>, Ken <tyl### [at] pacbellnet> 
wrote:

> It would really help if you could provide a short example of the code
> you are working with that would illustrate the problem and thus help
> us isolate it for you.

Ken,

Thanks.  I'm sorry it's taken so long to get back to this, but, you 
know, POV sort of gets squeezed into the cracks of my life, not vice 
versa.  

I've posted a couple of images over on p.binaries.images that illustrate 
what I'm talking about.  I'm modeling a starship, and when I do the 
superstructure paint as a y-gradient pigment, thus:

#declare t_Layers = texture {
   pigment {
      gradient y
      scale 2.26
         pigment_map {
            [0.0 p_trek_31 ]
            [0.90 p_trek_31 ]
            [0.90 p_trek_30 ]
            [0.999 p_trek_30 ]
            [0.999 p_trek_31 ]
            }
         } // close pigment
         
      }; //close texture t_layers

(using Jeff Lee's Trek pigments, which he was very kind about sharing), 
in the front orthographic view, the image comes out fine.  (Figure 1).  
You can see that the structure goes up further than the pigment in 
question, btw, which becomes important in a moment.

The front view (figure 1) uses an orthographic camera set up as follows:

camera { 
   orthographic
   location <0, 10, 175>
   look_at  <0, 10, 0>
   up <0, 0, 85>
   right <255, 0, 0>
   }

Everything looks fine.  But then, when I render my top view (figure 2), 
the y-gradient pigment vanishes, and you can see the inside of the hull.  
(The darker grey lines are the 'inside' of the structure which projects 
from the bottom of the hull.  It took me a while to figure out what I 
was looking at, there. 8) )

The top view (figure 2) uses an orthagraphic camera set up as follows:

camera { 
   orthographic
   location <0, 60, 0>
   look_at  <0, 0, 0>
   right <255, 0, 0>
   up <0, 382.5, 0>
   }

The other pigment in the y-gradient still appears, which puzzles the 
heck out of me.  Also, the superstructure's top element, which is not 
gradient textured, still appears, which tells me that I haven't set the 
camera too close to the model.  (I made that mistake on a previous 
model, and couldn't figure out for the longest time where the back end 
of the nacelles had gone, or why changing the light levels didn't change 
what I was seeing. *^.^* )

When I make a one-tenth unit adjustment to the position of the camera, 
setting it up like this:

camera { 
   orthographic
   location <0.1, 60, 0.1>
   look_at  <0, 0, 0>
   right <255, 0, 0>
   up <0, 382.5, 0>
   }

I get figure 3, in which the pigment is back, but the angle is kind of 
odd.

Why does it do that, and how can I make it stop?

(remove spamless from address to reply via email)

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