Celestia Forums

Celestia would really benefit from dynamic lighting. When is is coming? Is it coming? How much more taxing will it be on hardware? and will it drastically increase size of download.

Celestia already has dynamic lighting.

Perhaps you could you explain in more detail what you mean?

--Chris

o i hadnt realized. thought it was some other sort of technique. so why dont objects such as rings cast shadows on planets. why dont objects such satellites and shuttles have refective surfaces and why dont they cast shadows on themselves. Such as a a wing shawdoing the fuselage of the shuttle. I hope this clarifies my query. thanks

Chrisr,
Allot of what you are asking is already in Celestia. Rings do cast shadows. But I don't believe objects can cast a shadow on itself as yet but I could be wrong.

The rings casting shadows in planets its only seen with very good video cards, thats why you may not see it...

my card is could enough for spetral lighting night side lights and all the other jazz turned on so it doesnt make much sense that the planet (saturn) casts a shawdow on the rng but the ring doesnt cast on shadow on saturn

...it doesnt make much sense...

I know, you are right, but thats the way celestia works... I can also see the same you see, specular, night, bum and normal, shadows on the rings, but no shadow in the planet. The is nothing to do , I think....

Anonymous wrote:my card is could enough for spetral lighting night side lights and all the other jazz turned on so it doesnt make much sense that the planet (saturn) casts a shawdow on the rng but the ring doesnt cast on shadow on saturn

The shadow of the planet on the ring plane can be modelled as a simple black ellipse. The shadow of the rings on the planet have to be derived as the intersection of a textured oblique elliptical cylinder and an oblate spheroid. I guess I'm not surprised that the second takes more sophisticated processing than the first.

Grant

could someone please post a picture of saturn's rings casting a shadow on the planet using their celestia. Thanks

granthutchison wrote:

Anonymous wrote:my card is could enough for spetral lighting night side lights and all the other jazz turned on so it doesnt make much sense that the planet (saturn) casts a shawdow on the rng but the ring doesnt cast on shadow on saturn

The shadow of the planet on the ring plane can be modelled as a simple black ellipse. The shadow of the rings on the planet have to be derived as the intersection of a textured oblique elliptical cylinder and an oblate spheroid. I guess I'm not surprised that the second takes more sophisticated processing than the first.

It's actually not too bad to compute ring shadows, but vertex programs and clamp to texture border color extensions are required.

A ray is cast from each vertex of the planet to the sun and it's intersection with the equatorial plane is computed. Then, the distance of the intersection point from the planet center is used becomes the one dimension ring texture coordinate. No explicit ellipsoid/cylinder intersection is required.

chrisr, here's an image showing ring shadows:
http://www.shatters.net/gallery/view_photo.php?set_albumName=celestia&id=saturn80

It's not the best illustration of the effect, since the Sun is nearly in Saturn's equatorial plane at the time of the image.

--Chris

A couple of other pictures of Saturn's ring shadows can be seen at http://www.lns.cornell.edu/~seb/celestia/gallery-001.html#5

chris wrote:It's actually not too bad to compute ring shadows ...

Which serves to remind me that I should only speculate about things I know something about .
I did once model Saturn in an old version of POVray, using a now-defunct "Halo" object to model the rings - it did good light scattering, so I was able to model forward- and back-scatter nicely, but it didn't cast a shadow on the planet. So I ended up with a monstrous hack involving cropped cylinders which I guess has scarred me for life ...
The final movie is a tiny little thing now, at modern screen resolutions: http://www.solarviews.com/cap/sat/vsaturn1.htm

Grant

I was thinking: what will happen if we put a 3d model replacing the rings? will it cast shadows in the planet??

I know celestia cant render object shadows on models, but I dont know about model shadows on other objects; although I'd tend to think not...

I ll try to do it and then tell you what i got...

Nope 3ds or cms objects can't cast shadows. Believe me i've tried!!

Stencil shadows for 3DS objects is a feature that I'm very excited to work on; it probably won't make 1.3.2. Hopefully the version after, though . . . Celestia needs some more eye candy. Imagine shadows from the struts and solar panels of the ISS, or a bump mapped, self-shadowing Eros!

--Chris

How about being able to have lighting on models in celestia.3Ds max models have the possibility of self-illumination.This could look great on space ships etc.When I have experimented exporting lights set around and in models in 3ds max and exported into Celestia -no self-illumination and no external lighting shows up but lights inside e.g.a tunnel or building there is some light in the scenes but it seems to come from the direction of the nearest star and as bright as the ambient light at that position in space.Yours Jestr