Shadow within a comet coma

#8

Glad to help, I played with it a bit (during some idle time I had yesterday) I added a smoker to the glow and pushed the coma back slightly (to account for the push of the solar wind). I am not happy with the (temporal) progression (drift and offset) that I have, it just looks to swirly, but with the smoker in the glow the render time increases substantially and I don’t have the time to discover what settings would look right.
It does however look ok in stills.

[img]http://idisk.mac.com/holderness/Public/Concept/comet_3.png[/img]

You will need to point the project to your local ubershape plug and bump shader (I didn't include) Turn off the smoker in the sun AND coma glow light to get reasonable render time when you don't need it .
[Project file](http://idisk.mac.com/holderness/Public/Concept/comet.prj)

PS I forgot to mention, negative light is a surreal concept to begin with, and this is an inverse use of it (the sun’s ray shadow in the glow is inverted to positive and then set to negative illumination) so taking a bit of effort to wrap your head around it is to be expected.

#9

Hi WmH,

I threw together a project using your recipe and it works great! For the “sun” light I set the Glow Intensity to -0.5 and the Glow Factor to 2.0. For the “coma” the Glow Intensity is 0.5 and the Glow Factor is 1.4. These values produce a realistic image and they avoid the abrupt disappearance of the shadow at the edge of the coma glow (seen in your original video).

Joe T

#10

Glad you are getting good results with it, however the shadow edge was likely related to the lights glow extents rather than to intensity or glow factor… I was just quickly scrapping the project together and set the reach of the suns shadow so that is was “for sure” inside the coma glow (as the reverse yields rendering artifacts).

You will find this “trick” sometimes requires fairly precise alignment of the two extents for a believable shadow (primary and negative glow) and that the negative must be “just short” of the primary glow extent or you will get artifacts.

#11

William you are amazing. Always comming up with the right answer… I remember couple months ago with the Storm challenge, your solution was excellent. How many tricks like that do you have up your sleeve…? I knew this shadow in a glow could be done as I have seen it before. The question as where…!

We should bring back an updated tutorials section on the upcoming New Ei Webside: “Old school trick that works perfectly well with recent EIAS version…”

Thanks for sharing your knowledge.

#12

I agree with Rick and I owe you one, William. A couple beers, if you’re ever in the area (Space Coast of Florida).

I found those artifacts you mentioned; even when the glow regions are precisely set, minor artifacts appear when the Camera is near the juncture of the shadow and the back edge of the coma. However, careful positioning of Camera avoids that and allows me to get a nice “sunrise” off the edge of the nucleus with a dramatic shadow!

Joe T

#13

Joe, would you care to post your final image or animation. Would be a nice conclusion to the thread.

#14

Thanks for the kind words Richard, I was a heavy user of EI 2.X and spent many nights knocking my head against the CRT. (perhaps why it stuck so long;-) Amazing that many of the old “tricks” still work and still hold up by todays (visual) standards (further proof how amazing EI really is)

No problem for the assistance Joe, just pay it forward; if sometime you see another EI user struggling and (think) you have an answer then take the few minutes to share.
I owe Bear for many hours that I would have spent struggling years ago if not for his always generous assistance.

And I agree with Richard it would be great to see some of the final product.

#15

Although it’s just a WIP at this time, here’s my cometary nucleus. The gas jets erupting from the nucleus are spotlights shining through smokers. I’ll probably add several more of these and they’ll be animated.

William & Rick, thanks again for your help.

Joe T
http://members.aol.com/astroscans/nucleus.jpg

#16

Theses are great Joe! Thermal expansion and floating debris are a nice touch. Congrats.

#17

Exceptional work! I love the tone of the images.

Look forward to seeing more! (We are greedy us users :wink:
Ian

#18

Richard and Ian, thank you for your nice comments on my images. It may be several weeks before I noodle this project into its final form. I’ll try to remember to post something when it is done.

Joe T

#19

Sorry, been too busy to post. Really nice image(s), hope to see your finished product. Amazing how convincing smokers can be given the current state of the art (for light passing through semi transparent objects).
In my minds eye I had always imagined comets would have been a bit more translucent with some subsurface scattering (like marble or a dirty snowball) but the (few) actual images taken of comets core’s show a form very (very) close to your model.
Question: what are the brighter reddish area’s in the shadow zone (particularly in image 2), is that glow or translucence or something else entirely?

#20

this is the best EI technique I ever seen…
Thanks for sharing! bookmarked

Loon

#21

Hi William,

Even though they are largely composed of water ice, comet nuclei aren’t translucent in any of the NASA or ESA images I’ve seen. However, only a handful of comet nuclei have ever been imaged at close range so who knows?

The brighter reddish patches on the “darkside” of my object are meant to be “active” regions on the surface. Today I added a gas jet that erupts from one of those red areas. In reality, the night-side of a real cometary nucleus would probably be as black as coal, but I have to “hollywood-ize” my stuff to keep it lively (thereby keeping my clients happy).

You are right about Smokers; they are very useful. There are eleven in my project so far, and I expect that number to increase.

See you later,

Joe T

#22

Hi All,

Here’s the update you requested (Ian). I don’t have the bandwidth for a nice video, so here’s a clunky animated GIF showing every 50th frame of my outgassing comet coma (minus the starfield). There are 18 gas jets (glow lights) each with its own uniquely configured Smoker. A Maya-using friend has already asked for an HDTV rendering of this for possible use in a show.

This wouldn’t have been so dramatic without the shadow technique William gave me - thanks again for that!

p.s. I am replacing the animated GIF with a 15fps QT movie.

Sincerely,

Joe
http://members.aol.com/astroscans/comet.mov

#23

very nice, but I would like to see a more FPS version…

for the bandwidth problem, you can upload to youtube or some other web brodcast if you don’t mind…

thanks for sharing

#24

Beautiful, i can understand the interest of your friend for an HDTV rendering. I think must be very interesting to see it in large size. I can´t imagine how you get those gas jets with the smokers, they really looks as particles with all the subtile details and twists of the gas. Great work.

FelixCat

#25

Hi Loon and Felix,

Thank you for your nice comments on my project. Loon, I’ll try to get a video up somewhere for you. I’m not sure I want to register with YouTube; it looks too crazy there for me. A few years ago, I registered with another edgy site and I cannot get off their mailing list.

Felix, in order to achieve all the different textures in the gas jets, I just used various settings on the glow lights and Smokers. If anyone would like to see them I could email a copy of my project. I’d have to substitute an uber-sphere for my asteroid, though. My asteroid is about 13 Megabytes in size and I still use an old-fashioned, dial-up internet connection!

Joe T

#26

Hi, Joe. Very kind of you for offering your project for study. I could be very happy if you can (when you have some time) send me a copy of the project. BTW would be a good idea to have some kind of projects repository in the Ei web site…
FelixCat

#27

Lets make our own… After all, the new EI site has a WIKI :slight_smile:

Great work Joe, I really hope you find a way to get a full speed version online :wink:

Again, damn fine stuff,
Ian