Hi Bill,

I'm familiar with the effects you mentioned, problem is I did
something so stupid I'm not even going to mention it. I'd tell you
it's the first stupid thing I've done in the ten years I've been
using Guide, but I have a sneaking suspicion you would never believe me! <G>

Larry

At 08:49 AM 10/13/2010, you wrote:

>
>
>Hi Larry,
>
> > Set the field to 180d and switch back and forth from zenith to
> > nadir. This shows a considerable diffference beteen the solid
> > "horizon color" circle size and the dotted "field circle"
> > size. Moving around the image shows all kinds of effects.
>
>Hmmm... if what you mean is "the area shown at the zenith is
>a bit bigger than the area shown at the nadir", then you're right,
>and there are two reasons for this.
>
>First, because of refraction, you can see a little bit below
>the horizon. So the portion shown for "sky" is a bit larger than
>that shown for "ground".
>
>And second, if your altitude is greater than zero, you get
>a bit of "horizon dip" and can see even _more_ sky, and the ground
>gets even smaller. (Set a higher altitude, and you'll see this
>effect exaggerated.)
>
>But as far as moving around image goes... I do see changes in
>the curve of the horizon, but that's just what is to be expected
>with a wide-field view. You get a sort of "fisheye" effect. As
>you move around, though, the ground ought to be filled in
>correctly and the sky not filled in. If your altitude is zero
>meters and the "Include refraction" box is checked in the Locations
>dialog, then as the cursor moves over the filled-in section, the
>altitude shown in the legend area should be negative; as the mouse
>cursor moves over the sky, that altitude should be positive.
>
>-- Bill

Laren Dart
http://ldart.got.net