Bald Eagle <cre### [at] netscapenet> wrote:
> Some of the yellow layout "lines" (and these are HUGE cylinders) also
> inexplicably disappear when I zoom out.  Rotate view y*90, and the other
> lines disappear!

The lines are disappearing under the effects of aliasing. This commonly affects
lines falling along the four cardinal directions (north, south, east, west). For
2D images such as yours, it's best to set the line thickness according to the
image's width or height. This can be done automatically:

  #declare LineThick = 2/image_width;

where "2" is the target thickness, in pixels. To get lines only a pixel in width
to show up, you'll need to slightly translate the line perpendicularly from its
own direction, like so:

  cylinder{
    -x, x, LineThick
    pigment{rgb x+y}
    translate y*1/image_height
  }

For zooming in/out, it's helpful to design your camera a bit differently and
alter the line thickness equation like so:

  #declare CamScale = 2;
  #declare LineThick = 2*CamScale/image_width;

  camera{
    orthographic
    right x*2 up y*2
    location -z*1e5
    look_at z
    scale CamScale
  }

The lines might still disappear if they are only a pixel thick, so it's best to
use thicknesses greater than 1 pixel.

Hope that helps!

Sam

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