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Forum » SpaceEngine » Feedback and Suggestions » Zero-Phase Glare (Feasiblilty in SpaceEngine)
Zero-Phase Glare
AtmoscatDate: Monday, 12.03.2012, 16:05 | Message # 1
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Hello SpaceEngineer,

would it be possible to have a Zero-Phase Glare effect in SE? It is the optical effect when looking at rough surfaces (very prominent on Earth's Moon) in down-sun direction, towards the anti-solar point.

For example it can be seen in this video of the descent of the Apollo 17 Lunar Module towards the surface.

http://footagevault.com/clip/FTV-0002383/apollo+17/hd

There's that bright spot which equals the anti-solar point (where the axis of the light-source (Sun) and the surface and the observer are in one line. The bright spot is most clearly visible, when the the shadow of the LEM comes into view when the shadow passes over a large crater ("Camelot") in the distance.

The Zero-Phase glare effect also happens on Earth and most of the airless moons.
Bjorn Jonsson recently created this nice rendering of Enceladus, it also shows beautifully the zero-phase glare effect at 03:04, I am not sure, how he did that (shaders or what?).

http://vimeo.com/37689757

Here's a few interesting links about this effect:

http://www3.telus.net/summa/moonshot/0phase.htm

http://articles.adsabs.harvard.edu/full....00.html

Any chance we could have this in SE? Thanks for looking!





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SpaceEngineerDate: Monday, 12.03.2012, 21:54 | Message # 2
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Hmmm, this is very easy - just add phase function. Can you find a formula describing it? In the last link I see a graphic, but there's no formula.

*





 
AtmoscatDate: Tuesday, 13.03.2012, 01:30 | Message # 3
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Quote (SpaceEngineer)
Hmmm, this is very easy - just add pahse function. Can you find a formula describing it? In last link I see a graphic, but there no formula.


Great, so it is possible! I have searched again for formulas about the zero-phase effect, the best canditate with functions, at least with the Moon as an example, I have found here (It is not easy to understand) but does that help? See first page (333), formula at the bottom right.

http://articles.adsabs.harvard.edu/cgi-bin....pe=.pdf

I'll keep on looking out for a good document, stay tuned. Thank you for considering the possibility of including the effect into your rendering code!

Edit: This page from LPOD does not have a formular, only a graph, but at the bottom there are several, maybe useful, links of documents.
http://the-moon.wikispaces.com/opposition+surge

Edit II: Bjorn Jonsson, the author of the Enceladus video above stated:
Quote
I'm using a slightly modified version of the earliest Hapke function - it's modified to avoid unrealistic effects when the emission angle approaches 90 degrees. The phase effects are interesting and very strong. I even had to reduce the opposition effect a bit to avoid problems with dynamic range.


All I could find so far about the scientist B.W. Hapke are these documents (not free):
http://www.sciencedirect.com/science/article/pii/S0019103500964546#bF1
http://www.sciencedirect.com/science/article/pii/S0019103504001939

Also this:
http://en.wikipedia.org/wiki/Hapke_parameters
http://en.wikipedia.org/wiki/Geometric_albedo

Okay, this is looking useful!:
http://selena.sai.msu.ru/Pug/Publications/ms42/m42_60.pdf





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Edited by Atmoscat - Tuesday, 13.03.2012, 04:32
 
SpaceEngineerDate: Tuesday, 13.03.2012, 14:37 | Message # 4
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Thanks, I will look at it today.




 
AtmoscatDate: Wednesday, 02.04.2014, 21:07 | Message # 5
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Hello SpaceEngineer!

Any chance this "feature" might make it into the next or nearest releases?

Keep up your great work!





PC: Intel® Core™2 Duo Processor E8500 @ 3.16GHz, 3.25 GB / 4.00 GB DDR3 RAM, GeForce GTX750Ti 2048 MB VRAM, WinXP Home 32bit / Windows7Pro 64bit
 
SpaceEngineerDate: Wednesday, 02.04.2014, 22:43 | Message # 6
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I didn't found an analytic formula for it. Links posted above have no usable formula.




 
Destructor1701Date: Thursday, 03.04.2014, 03:01 | Message # 7
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Isn't it just a feature of the orientation of light and shade?

Shouldn't it naturally happen in SE without any special coding - it's just when the angle you view the landscape from matches that from which the light is coming, and so the lit surfaces entirely occlude the dark surfaces at the anti-solar point, making that area seem brighter overall?





 
HarbingerDawnDate: Thursday, 03.04.2014, 04:34 | Message # 8
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No, because unlike reality, SE does not have unlimited level of detail down to microscopic scales at all times. A lot of the shading going on in real life that contributes to this effect is due to things such as grains of dust shading each other, which SE obviously can't actually do; therefore, it can only be approximated using some formula. If no one can come up with a usable one for him to implement, then it won't be done.




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SpaceEngineerDate: Thursday, 03.04.2014, 09:51 | Message # 9
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Moon have lighting model based on this (full Moon looks like uniformly lighted disk), but it work only if observer is far away.




 
Destructor1701Date: Saturday, 05.04.2014, 13:04 | Message # 10
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Ah, neat-o, thanks for the explanation, guys.




 
Forum » SpaceEngine » Feedback and Suggestions » Zero-Phase Glare (Feasiblilty in SpaceEngine)
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