Drawing a better star

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krishnafbgroup
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Post #81by krishnafbgroup » 28.02.2018, 08:28

Yes fact, with glare described as a Gaussian, extremely bright stars did not look like the ones in your image. With a Gaussian, the edges of the star get sharper as the brightness increases. This matches what we see for the core PSF, but the glare behaves differently.

Here's a very relevant paper titled "Physically-Based Glare Effects for Digital Images": http://citeseerx.ist.psu.edu/viewdoc/do ... 1&type=pdf

The authors describe the PSF for the eye as the sum of three terms: a central Gaussian, a theta^-2 term, and a theta^-3 term (where theta is the angle from the center of the light source.) Here's a sample image of the Southern Cross where Gaussian glare is replaced by G(1/(1 + k*r^3)), where G is the glare brightness, k is a constant that sets the glare falloff rate, and r is the distance in pixels. I deliberately did not the angular distance, as it's more desirable to resolve stars at high zoom factors than it is to try and realistically reproduce all the quirks of a real imaging system (and I realize that's what I did with the diffraction spikes, but they're aesthetically pleasing :) ).

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mmontag
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Post #82by mmontag » 09.04.2018, 22:28

Is anyone currently working on this? I would love to contribute to Celestia and maybe hack on this as my first entry into the void. I will be looking around the forum to try to figure out what the current state of the project is, whether Chris is still involved, etc. Is the github repository now the canonical source?

krishnafbgroup wrote:Here's a very relevant paper titled "Physically-Based Glare Effects for Digital Images": http://citeseerx.ist.psu.edu/viewdoc/do ... 1&type=pdf

The link is broken, but here's another copy:

http://luthuli.cs.uiuc.edu/~daf/courses/rendering/papers3/spencer95.pdf

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Alexell M
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Post #83by Alexell » 28.05.2018, 23:41

mmontag, Hey. Chris will not return to the project. At least that's what he told me. Of the old developers, no one particularly expressed a desire to return to the project. Now we are developing Celestia by the forces of not indifferent people on Github. We will be happy if you will help with programming.
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chris
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Post #84by chris » 01.06.2018, 17:49

I'm afraid that I'm still too busy for Celestia development, but here is what's possible with the new Gaia DR2 catalog:

holeintheheavens.jpg


This is an area the central Milky Way blocked by dark nebula Barnard 86 ("Herschel's Hole in the Heavens"). Nearby is open cluster NGC 6520.

No 3D information was used in this image—stars were rendered just using RA, declination, magnitude, and color index. The task for Celestia developers working with Gaia DR 2 is much more formidable, but definitely doable!

Cheers,

Chris

john71
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Post #85by john71 » 02.06.2018, 17:26

Chris, it is very good to hear from you again! :)

You + Gaia DR 2 in the same post - it is too good to be true.


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