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AdamMc
Planets
on Sep 22, 2007 at 10:12:06 pm

Hi,

I have a few questions here so apologies in advance for the long post, i realy would appreciate your help or advice. A while ago i posted and recieved a great answer about how to create an earth so that the light side had a daytime texture and the dark had a night texture with city lights showing. The answer was to use a luminance node pluged into a ramp with day texture in one position and night in the other, so that when there is a lot of light hitting the planet the day texture will show and when there is little or no light hitting the sphere the night texture will show up. This is great, only if there is no light you cant see the night texture! Is there any way around this or any other technique i could use? I would like to animate time moving fast forward just like in the 'Always HD' advert to the right.

My other question is about the atmosphere of the planet. I have a slightly larger sphere with a glow and the facing ratio of a sampler info node pluged in to a ramps v coord which is then pluged in to the transparencey of the atmosphere to give it the denser look around the edges where there is more atmosphere to see through. When i shine a light on the planet the dark side will still have a bright atmosphere. How do i correct this?

One more quick question; When i do a render at a fair distance away from the planet, the atmospheres glow stays the same size so the fade out at the edge becomes so soft you can hardly see it. When you are just above the atmosphere it is a very abrupt fade. Is there a different way to create atmospheres so that this wont happen?

Thanks for you help!
Adam


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Steve Sayer
Re: Planets
on Sep 28, 2007 at 2:39:52 pm

Hi, Adam. Sorry for the long delay; I hope I can give you some useful pointers.

First, the two textures: you want the night-time texture to be plugged into the incandescence channel, not the colour channel, of the material. (I assume your night-time texture portrays the glowing lights of cities etc.) Use the surfaceLuminance node to control the blender attribute of a blendColors node, mixing the night-time texture with pure black.

I did a quick test, and in order to get the best results, I increased the intensity of the 'sun' light while lowering the planet's diffuse attribute (this produces a sharper terminator around the planet). Then I used a clamp node to limit the output of the surfaceLuminance node to values between zero and one (otherwise the night-time texture starts to get mixed back into the day-time texture in places where the luminance is above 1).

You can just leave the regular day-time texture plugged into the colour attribute, since it will be invisible on the shadowed side anyway.

As for the atmosphere, I think the quickest solution is to open the 'Render stats' section of the atmosphere's shape node, and uncheck 'Double Sided.' This will prevent the inside of the sphere from receiving light--and that's what's causing the glow to be visible on the night-time side.

Finally, I think the problem with the glow behaviour has to do with 'Auto Exposure.' Select the shaderGlow1 node in your Hypershade, and see if it has 'Auto Exposure' checked. If so, Maya will make changes to the glow properties each time you render a frame, trying to guess at the best exposure for the glow. But if you want the glow to be consistent for one object in an animation while the camera approches or recedes from it, you need to turn this off. When you do so, you will probably find the glow very overexposed. Tweak the values manually until you get the look you want, and then things should stay consistent as you move the camera away from the planet.

Hope that helps! Good luck.

-Steve


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AdamMc
Re: Planets
on Oct 7, 2007 at 5:13:12 pm

Steve,

A massive thanks for your time and help, it has worked a treat!

Many thanks,
Adam


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lacrossjumper
Re: Planets
on Nov 18, 2007 at 7:06:30 pm

wait how did you make the atmosphere to start with?

thanks


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