The problem is that the Cartesian system of describing a 3dimensional space doesn't
allow for proper calculations when the
camera points straight down like that. The up vector goes from y to <0,0,0> and
rotations are mathematically impossible. I
don't have all the mathematical details here, but the calculations jump to infinity in
this situation. My brother works with
aerodynamics and he had to work around this by using quaternions.

Josh

Dawn McKnight wrote:

> Someone recently posted on here that a crash is always an error; that
> the appropriate action for the program to take if there's something
> wrong is to give an error message, not to crash.  So I'm posting this
> code, which makes POV do just that.
>
> I am using POV-Ray, version 3.1g for Macintosh, on a G3/300 running OS
> 9.0.4, with 160mb RAM.  I know code shouldn't normally be posted in this
> group, but this is /really/ short, as I was looking at how height fields
> work.  I suspect my slopes are too abrupt or too confused, but here it
> is.  You can find the image I was using to create the height field at
<http://www.coyotesdaughter.com/dawn/newworld.gif>.
>
> #include "colors.inc"
>
> light_source { <0, 10, 0> White }
>
> camera {
>         location <0, 3, 0>
>         look_at 0
>         } // close camera
>
> height_field {
>         gif
>         "newworld.gif"
>         //smooth
>         pigment { Red }
>         }
>
> --
> Dawn McKnight      | "Who cares what the hipbone's connected to? I'm in Neurology!"
> McK### [at] maccom   |                                    -- Justine Devlin, M.D.

--
Josh English -- Lexiphanic Lethomaniac
eng### [at] spiritonecom
The POV-Ray Cyclopedia http://www.spiritone.com/~english/cyclopedia/

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On Mon, 27 Nov 2000 19:23:13 -0700, Dawn McKnight <mck### [at] maccom>
wrote:

<snip>

>camera {
>	location <0, 3, 0>
>	look_at 0
>	} // close camera

I am almost certain this appears in the POV-Ray documentation. At
least I am certain I knew it long before I started frequenting this
server. Basically, when the direction vector is parallel to the y
axis, there's a high chance of a division by zero error. This happens
because the default sky vector is +y and POV gets confused when it
tries to determine the transformation matrix to apply to the camera.
Try moving the camera location or look_at just a bit (1E-6 in x or z
is enough), using an up vector of +z (yuck!) or just placing your
object in the xy plane instead of xz, and then using a more common
camera such as camera { location -3*z }


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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Another solution is to not use the look_at keyword
and instead use a direction statement in the camera
block and then rotate/translate the camera as needed.
This also allows more control of the camera.

camera {
  location 0            // leave at 0 so rotation works as expected
  direction <0, 0, 1>   // look along the Z axis in the + direction
  right <640/480, 0, 0> // change depending on output image dimensions
  up <0, 1, 0>
  rotate WHATEVER
  translate WHEREEVER
}


Of course, right, up, and direction must be mutally perpendicular.

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