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