I'm still not getting this in my mind right.  Seems like a sort of
perspective camera to me, like say you were wanting a rectangular
region of 4x3 units at 0 z then double that at 1 z (8x6) and half that
(2x1.5) at -1 z.... am I even close?
Someone is bound to have a better grasp on your concept than I so
don't despair : ) just yet anyway.
To let you know what I'm thinking this would be like I'd have to say
it's a slice of 3D turned to one side a bit.  If so why not use
orthographic on a rotated section of a model?  I may be way off about
this, I know, so sorry if I'm confused.

PS  see p.b.i. for J. Grimberts demo gif.

Bob

J. Grimbert <jgr### [at] atos-groupcom> wrote in message
news:37D3A158.9E7A5019@atos-group.com...
> Previously in povray.advanced-users, but here due to the attachment.
>
> Bob Hughes wrote:
> >
> > This may be obvious to others as well, I can't make out your
intention
> > exactly.  I'd suggest posting a drawing if you could.  I'd suggest
> > HTML formatted posting but that's NOT a good idea since people
have a
> > difficult time with them.  Also I flunked out of being a
> > "advanced-user" so I probably shouldn't even be here.
> >  ; b
>
> My intention would be for example to model a diesel engine in pov,
> and then cutting it with a plane (or a box)... to obtain the
> perspective image one can see in a industrial drawing class room,
> where the x and y dimensions are kept, and the right angle too,
while
> dimension in the z are projected in a parallele perspective.
> (see the attached gif)
> The ray are parallels, like with the orthographic camera, but
> unlike the orthographic camera, the <1,1,1> point is not hidden by
> the <1,1,0> point  (rather the <2,2,0> or the <1.5,1.5,0> )...
>
> I may defined it like a sort of oblic orthographic...
>
> So my question remains:
>
> Have anybody any suggestion on how to achieve that ?
>  (with all pov-object, of course, not only the box).
>
> >
> > Bob
> >
> > J. Grimbert <jgr### [at] atos-groupcom> wrote in message
> > news:37D38620.7E9E491A@atos-group.com...
> > >
> > > I would like to use pov to render a view like the
> > > own drawn below for a box
> > >
> > >   +--+
> > >  /  /|
> > > +--+ |
> > > |  | +
> > > |  |/
> > > +--+
> > >
> > > It's just the classical 3D technical drawing...
> > > It looks like the orthographic camera, but
> > > increase of the z is transformed as p*(x+y),
> > > with p either 1/2, 1 or 3/4 ...
> > >
> > > Have anybody any suggestion on how to achieve that ?
> > >  (with all pov-object, of course, not only the box).


----------------------------------------------------------------------
----------

Post a reply to this message

Bob Hughes wrote:
> 
> I'm still not getting this in my mind right.  Seems like a sort of
> perspective camera to me, like say you were wanting a rectangular
> region of 4x3 units at 0 z then double that at 1 z (8x6) and half that
> (2x1.5) at -1 z.... am I even close?

Not at all. the 4x3 stay always the same apparent size, at 0 z, -1 z or
1 z,
but using (u,v) coordinates for the rendered pictures, (v is up), i
think
the correlation is somethings like this:

 u = x + p.z
 v = y + q.z

so that xyz<0,0,0> is at say uv<0,0>
xyz<2,0,0> is at uv<2,0>
but xyz<2,0,2> is at uv<3,1>

whereas the orthographic camera would have given for xyz<2,0,2> the
uv<2,0>

In fact, there is no perspective points or lines: all the rays are
really parallele
(thus the apparent size do not change with the z, just like the
orthographic camera),
but instead of a full face compression, you have a partial look of the
depth.

> Someone is bound to have a better grasp on your concept than I so
> don't despair : ) just yet anyway.
> To let you know what I'm thinking this would be like I'd have to say
> it's a slice of 3D turned to one side a bit.  If so why not use
> orthographic on a rotated section of a model?  
Well that's may be the idea, 
The <x,y,0> should really be directly seen as <u=x,v=y>, keeping the
lengths
and the right angle.

In fact, It seems I need to have a direction which is not perpendicular
to
the image right and up. 

Eh! that's it. I just remove the look_at and it works !!!!
(ok, with a warning about the non perpendicular, but that's what I
want!)

my camera is (for full cabinet)
camera
{ orthographic
  location  <40.0, 40.5, -40.0>
  direction <-1,-1,1>
  up        5*y
  right     5*4/3*x
  //look_at   <0.0, 0.0,  0.0>
}

I will post a rendered image in p.b.i soon

>I may be way off about
> this, I know, so sorry if I'm confused.
> 
> PS  see p.b.i. for J. Grimberts demo gif.
> 
> Bob
>

Post a reply to this message

I had the same question a few months ago.  Check out
http://www.dlugosz.com/POV/another_world.html for a "half cab" effect and
notes as I go.  I ended up shearing whole scene, not the camera, because
non-ortho cameras don't optomize the speed of the trace.  If this is what
you are looking for, I'll elaborate on the technique I used.

--John


> > > J. Grimbert <jgr### [at] atos-groupcom> wrote in message
> > > news:37D38620.7E9E491A@atos-group.com...
> > > >
> > > > I would like to use pov to render a view like the
> > > > own drawn below for a box
> > > >
> > > >   +--+
> > > >  /  /|
> > > > +--+ |
> > > > |  | +
> > > > |  |/
> > > > +--+
> > > >
> > > > It's just the classical 3D technical drawing...
> > > > It looks like the orthographic camera, but
> > > > increase of the z is transformed as p*(x+y),
> > > > with p either 1/2, 1 or 3/4 ...
> > > >
> > > > Have anybody any suggestion on how to achieve that ?
> > > >  (with all pov-object, of course, not only the box).
>

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