Rassilon wrote:This is going to be cool...
On shadows...eclipse shadows dont cast them right?
Nope. What happens is that Celestia thinks that the ring is actually a spherical planet located more or less right next to the star, so half of the ring is in "day" and half is in "night". Same is true for the shadow squares.
Hmm. It also occurs to me that Celestia thinks that the shadow squares are in exactly the same orbit as the ringworld itself. They'll never cast shadows on it that way, even if the lighting on the ring worked right... doh.
I assume the lighting problem would be a fairly tough fix. While it is relatively simple to trace a single ray from a mesh's origin to the primary's origin to determine if something is eclipsing it (which I assume is how Celestia goes about it), this obviously doesn't work for a proper Ringworld.
Any solution I can immediately see that doesn't require changes to the model would require ray calculations from several points all along the inner circumference, which slows things down.
I
could change the model so that each short segment of the Ringworld was an independent object merely sharing the same orbit as the other segments (just like I may do for the shadow squares). But I think spreading them out along the orbit might be a bit tedious (I'm just assuming it is possible; I don't know), and the resulting object would probably have ugly seams and gaps.
This lighting problem seems likely to exist for any sort of structure that surrounds a star in Celestia rather than orbiting it, such as a Dyson sphere. It'll be lit precisely like an inside-out planet. (And the solution gets even slower for a Dyson Sphere, since you have to account for rays traced along the vertical circumference as well as the horizontal.)
There are some other problems with objects of this type that I didn't mention:
The first is with the "click on an object to select it" system. There probably isn't a problem if you have a Dyson Sphere, which is close to the size of its bounding box, but with Ringworld, it interferes with selecting stars that are quite obviously not anywhere near the object. It also prevents you from click-selecting anything inside the ring, at least if the camera is not physically inside as well. The only fix I can think of is to test whether polygons of the mesh actually lie at the point the user clicked, once we have determined that they clicked inside the bounding box.
The second problem has to do (apparently) with the order in which that Celestia draws objects. Ringworld's radius is just larger than Earth's orbital radius. When you are looking at Earth, sometimes the planet disappears into/behind Ringworld even though it should be in front of it, and vice versa. Again, this is probably because Celestia believes the ringworld to be in a much closer orbit to the star than the mesh indicates. The order also seems to change depending on whether the object is selected.
Finally, Celestia seems to use some sort of far clipping plane thing. The result is that when you look at the "Great Arch" that the ringworld is supposed to produce as seen from its inner surface, a largish section directly opposite the star from your position is not drawn because it is too far away.
The only other downfall is not being able to add an atmosphere and cloud cover...Now that really be awsome!
btw, Do you need a texture for it?
Well, if you want to do one, sure. I could probably do one myself, but I really have much more interest in making the thing and getting it to show up reasonably than in polishing it off.
By the way, the Ringworld right now is literally just a ring. I haven't attempted to model the rim walls or any sort of structures other than the squares (I didn't have the one book in the series that I own handy, and it may even be unnecessary due to the scale of the thing). While it is to actual scale in diameter and in the width above and below the ecliptic, it is not to scale as far as cross sectional thickness goes. I just wanted to get the thing working first.
Incidentally, I happen to have lying around on my harddrive a partially completed model of Arthur C. Clarke's Rama spacecraft (cf. Rendezvous with Rama). It would be fairly simple to convert it to 3ds and put it in Celestia. But it'd be pretty dark without some sort of internal light source to mimic the linear suns, so I may hold off on that. From the outside, Rama is pretty much just a big spinning cylinder with some bumps on the end, and that's not terribly interesting.
Other things I've considered making are Babylon 5 and a Crystal Shell style solar system ala the old TSR Spelljammer setting (flat or hemispherical planets, platonic solids as planets, etc).
Your guess is as good as mine as to which I actually have.
