Planetshine

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chris
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Planetshine

Post #1by chris » 17.03.2008, 23:53

Since the topic of planetshine has come up, I thought I'd show some of the progress that I've been making on this feature:

Image

No ambient light is enabled. The bluish light on the bottom of Hubble is being reflected from the Earth. This is the OpenGL 2.0 render path, but you can see similar results even with basic rendering.

It's working quite well in most situations, but there's still quite a bit more work required for this to be robust enough to commit to SVN.

--Chris

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Post #2by chris » 18.03.2008, 00:08

The night side of Enceladus faintly illuminated by Saturnshine:

Image

--Chris

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Post #3by ElChristou » 18.03.2008, 00:43

Really stunning! 8O
Image

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Post #4by chris » 18.03.2008, 02:17

Runar's Buran in Flight add-on with planetshine:

Image

--Chris

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Post #5by rra » 18.03.2008, 11:31

this is already very impressive, Chris

one question:
will the planetshine (implicitly) include also "moonshine" ??

Ren?©

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Post #6by Hungry4info » 18.03.2008, 11:43

chris wrote:Image

O_O Very nice!!

Is there a code in the .ssc to determine the colour and brightness of the shine? Or is it derived from the preexisting "Color [ R G B ]" and Albedo?
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Post #7by The Singing Badger » 18.03.2008, 16:02

This blog posting describes a photo of Enceladus being lit by Rheashine, Tethyshine and Dioneshine:

http://planetary.org/blog/article/00001360/

Is this possible with Celestia?

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Post #8by chris » 18.03.2008, 17:14

Hungry4info wrote:Is there a code in the .ssc to determine the colour and brightness of the shine? Or is it derived from the preexisting "Color [ R G B ]" and Albedo?


The albedo and color are all that are needed. The color property in an SSC definition is essentially the global average color of the texture map, which is what we want for planetshine. (We could do something more sophisiticated and actually use the texture map colors, but it's a lot of extra work for what would typically be minor visual differences.)

--Chris

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Post #9by chris » 18.03.2008, 17:21

The Singing Badger wrote:This blog posting describes a photo of Enceladus being lit by Rheashine, Tethyshine and Dioneshine:

http://planetary.org/blog/article/00001360/

Is this possible with Celestia?


Not at the moment. The current code doesn't consider light bouncing from moon to moon. It's not hard to add this, but it does require extra calculation, and in most cases such light is imperceptible--the Cassini imaging team used quite a long exposure time to capture that Enceladus image. Once Celestia supports high dynamic range rendering, these effects will be interesting.

--Chris

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Post #10by ajtribick » 18.03.2008, 17:38

...I wonder how significant planet-planet reflections would be in some of the more compact solar systems out there, e.g. Gliese 876.

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Post #11by chris » 18.03.2008, 17:58

ajtribick wrote:...I wonder how significant planet-planet reflections would be in some of the more compact solar systems out there, e.g. Gliese 876.


Interesting question . . . I've got some debugging code that displays irradiance from planet-moon reflectance as a fraction of solar irradiance. I'll try implementing planet-planet reflections and see what happens. My hunch is that not much light gets reflected from planet to planet: the irradiance of light reflected from a planet falls off with 1/d^2, where d is in units of radii of the reflecting planet. A quick look at the Gliese 876 system suggests that the planets will never get within 10 million kilometers of each other.

--Chris

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Post #12by CAP-Team » 21.03.2008, 10:07

Is planetshine already implemented in any SVN version? :mrgreen:
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Post #13by chris » 21.03.2008, 17:05

CAP-Team wrote:Is planetshine already implemented in any SVN version? :mrgreen:


Not yet . . . There are still a couple things that need to be fixed.

--Chris

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Post #14by chris » 26.03.2008, 03:10

Some further progress on planetshine . . . Here's an image of Cassini during Saturn orbit insertion in 2004. The spacecraft is illuminated by both the Sun and Saturn--so close to Saturn, the illumination from the planet is very apparent.

This image represents a significant accomplishment: Cassini is defined in its ssc file with an orbit about the Sun. Celestia doesn't just assume that light is reflected between orbitally bound objects any more. I added some new code that does fairly complicated tests to determine what objects may potentially illuminate objects in view. As is frequently the case in Celestia, the complexity arises because of the need to do things very fast, in this case lighting.

With Cassini, secondary illumination can come from a number of different bodies:
- Earth at launch and during gravitational assists
- Venus during gravitational assists
- Saturn during orbit insertion
- Titan and other Saturnian moons during encounters

It's really neat to watch the orange glow of Titan appear on the spacecraft as it performs a flyby of the Moon.

Image

--Chris

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Re: Planetshine

Post #15by ElChristou » 26.03.2008, 11:05

Very nice! Cannot wait to test this! :D
Image

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Re: Planetshine

Post #16by Hungry4info » 26.03.2008, 13:05

Indeed! This is truly awesome!

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Re: Planetshine

Post #17by Chuft-Captain » 27.03.2008, 02:25

That's awesome Chris!

... Just one question... will this include illumination by Mirrors? (You know what I'm talking about! :wink: )

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Re: Planetshine

Post #18by Chuft-Captain » 27.03.2008, 02:36

Sorry for the off-topic, but for some reason BBCode is OFF for me in this (Developer Talk) forum.
All is enabled in my profile, and works OK in other forums, but not here. Is this a bug in phpBB3??

eg: :wink: 8) :lol: :) :sad: <--- these should display as images (other people seem to be OK)

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Re: Planetshine

Post #19by chris » 27.03.2008, 03:09

Chuft-Captain wrote:Sorry for the off-topic, but for some reason BBCode is OFF for me in this (Developer Talk) forum.
All is enabled in my profile, and works OK in other forums, but not here. Is this a bug in phpBB3??

eg: :wink: 8) :lol: :) :sad: <--- these should display as images (other people seem to be OK)

Strange . . . Those permissions were indeed turned off. I had no idea that they were even settable per forum. BBCode and smilies should work now.

--Chris

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Re: Planetshine

Post #20by chris » 27.03.2008, 03:24

Chuft-Captain wrote:That's awesome Chris!

... Just one question... will this include illumination by Mirrors? (You know what I'm talking about! :wink: )

I'm afraid that it won't right now. The planetshine code only considers diffuse reflections, and it treats all light reflectors as spherical.

--Chris


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