Thursday, November 23, 2006

Unheavenly Bodies

The sun and moon in Second Life are unrealistic and just plain ugly.

That's right, I said it. I went there. Ugly!

Figure A.


As I see it, there are three main problems with Second Life's sun and moon:
  1. Their reflections on water stretch unrealistically.
  2. They sometimes appear as dark or darker than the sky around them.
  3. Background stars are drawn in front of them.
Examine Figure A; the left half is raw, untouched snapshot of a near-sunset in SL at 300m; the right half is what I think it should look like. (NB: the bottom of the reflection is partially obscured by clouds.) Both problems 1 and 2 are in full force here.

Figure B.

Optics minilesson #1: In the real world, a reflection of the sun or moon on the water appears stretched because of small irregularities (i.e. ripples) on the surface of the water which change the angle at which light is reflected. You can see this in Figure B, a test image I rendered in Blender using raytraced reflections. The image shows a lit sphere resting on a perfectly reflective surface. On the left side, the mirror is completely smooth; note that no stretching occurs in the reflection. On the right side, however, the mirror has small ripples which affect the angle of reflection, causing the same type of stretching seen in the real world.

My graphics card is not powerful enough to enable fancy water, so I, like many Residents, simply see an upside down and yuckily stretched version of the sun or moon in the water. I know the programmer who did that meant well—he or she just wanted to make it look as if there were ripples distorting the reflection. But all it accomplished was making it look like the Grid is a concave Discworld.

Optics Minilesson #2: In the real world, the sun can never appear as dark or darker than the surrounding sky for the simple reason that the brightness of the sky is due to partial scattering of the light from the sun. Most of the light from the sun passes through the atmosphere without much scattering, which is why the sun appears to be a circle with definite edges, rather than a vague patch of brightness.

Figure C.

Optics Minilesson #3: The moon, too, will always appear at least as bright as the sky around it, never darker (as it does in the left half of Figure C). This is especially obvious on days when the moon is visible during the early morning or late afternoon; the unlit parts of the moon, which would appear black at night, appear the color of the sky.

Why does this occur, when mountains and skyscrapers do appear dark against the sky? Quite simply, because mountains and skyscrapers block the scattered light from the sky. The moon, because it is outside the atmosphere, does not block it.

Also note in Figure C the star appearing in front of the moon. That's just crazy.

2 comments:

Akela Talamasca said...

*ominously* That's no star. It's a space station.

Patience said...

And since you're on the subject, I'd give my left pinky finger (well, Pati's...) for moon phases.