View Full Version : Physical sun and sky animation

01 January 2011, 06:37 PM
Hey, I am experimenting with the physical sun, making a timelapse that shows sunset and sunrise over about 100 frames. But I must be doing something wrong, animating the sun (directional light) because the rendering shows only the same dull picture no matter what frame I am rendering. Surely there most be some simple explanation that I have overlooked. Any suggestions?

Anyone wants to show a homemade tutorial on how to get the best result of the physical sun and sky doing this kind of animation changing from daylight to nightlight??

02 February 2011, 09:18 AM
I'm not sure this is the case here, but translation and scale do not affect mr skylight, only rotation.

02 February 2011, 02:49 PM
Thanks for your answer Rick, I know that I use only the rotation, I think my fault was a combination of different factors. It is a scene that I have been working on before, and had textures and shaders in a different folder, so that there actually where no place for the light to reflect.

But there has to be more, maybe a mental ray portal light would help?

I have troubles getting my shadows to show aswell, I set depth map shadows, but with physical sky, I guess ray trace shadows is what I need, I will have to try some more:)

02 February 2011, 11:00 PM
Now that I think of it, there is an option in mr sunlight to show a "sun disk", so when I said that translation does not affect anything, maybe I was wrong. Look in the mental ray documentation, I know there is a section on that topic (sun disk, sun glow, whatever).

Ok, I opened my books and I found the awnser... I've learned a great deal of things I didn't know too, hehe thanks to you ;)

So, in order to produce a timelapse light system in mental ray you must understand that the sun position (the sun disk) is set by the rotation of the light icon. I assume that you work in maya, or that it is the same in 3DS/XSI.

Delete your sun sky system and create a new one, so you will have the default values
First try to rotate the sun icon directly perpendicular to the ground, as if it was 12:00pm. Look up with your camera and render, you see the sun disk? Yes, and the mood is full blue sunny day, if you have objects and a ground in your scene, there should already be some shadows, don't change any values yet!!!

Now rotate the sun 45 degrees and find it with your camera in the sky, you see that even if the sun icon does not move, rotating it changes the sun's position... and the light mood! The sun is now more towards a red hue, and it has changed in position directly inversed of the rotation direction. Rotate it again 95 degrees from the original angle (like a 10:00pm setup), and now it is night, and the sun has gone away in tint, luminosity and position.

All you need now is to animate the rotation to place the sun where you need it in the sky, and change the values as you would like it to appear (glow, intensity, sky... aerial perspective -huh? what's that word?...). The rest of the awnsers and details in the "mr shaders: Sun and Sky" page of the documentation. Learn how to use the aerial perspective, you will thank me a lot ;) the rest is your effort to make my friend!

02 February 2011, 11:07 PM
no place for the light to reflect.
This should be automatic, mental ray raytracing produces all the reflect refract processing automatically, maybe you should consider using mia_x.

But there has to be more, maybe a mental ray portal light would help?

Portal lights are used for interior lighting only, it redirects the sun intensity you will find all the details again in the mental ray documentation

I have troubles getting my shadows to show aswell, I set depth map shadows, but with physical sky, I guess ray trace shadows is what I need, I will have to try some more:)
Don't modify the shadows options at all. If you want, use the raytrace shadows, Depth map sucks in my humble opinion (and I don't understand them well I must admit). If you need softer shadows, increase the shadow softness in the physicalsun tab, as well as the samples value.

02 February 2011, 07:11 PM
Thank you so much for your help RickT, I must say I have learnt a lot on mental ray and physical sun since I posted my question here! And I am happy that you did too;) Well, I did as you said, I quit my old physical sun and created a new one.

The thing is, rotation seemed to work fine, but the thing you wrote that made me find the problem and the solution was: aerial perspective. Under aerial perspective in mayas help, I found that when it comes to interior lightning by the physical sun through windows, (and I am sorry if I seem really stupid not to have known) the scene needs a few more inputs to be able to show the interior as it is supposed to look different times of the day.

I seemed not to have enough bounce from the sunlight onto my interior (sorry that I seemed to miss out on this very important fact about my scene), so this is why my scene got so incredibly dull.
A combination of portal lights, Global Illumination and new final gathering settings helped me creating the most wonderful daylight aswell as nightlight in my scene, and I am just really really happy about it.

So thanks again for making me look in ways that I would not have looked had it not been for your key note: aerial perspective!

02 February 2011, 08:20 PM
As far as I know, aerial perspective is to create fog and haze in your horizon, it is a kind of incredibly fast and simple participating media.

A portal light is the solution in mental ray to illuminate properly an interior scene, as the portal light recaptures the "energy" of the mental ray sun and distributes it in a room like a window. If you don't use portal lights when you render an interior scene lighten up with a skylight you will have to enter ridiculous values in the sunlight to have enough light, and it won't balance very well.

I am not sure you understand completely the aerial perspective "effect" yet, but you'll be very happy when you do... It creates a very realistic 3D haze in your scene in just a few clicks. What you needed here was the portal lights, so you can light up your interior with the sunlight/skylight system.

02 February 2011, 10:30 PM
Yes, you´re right, I don´t really understand yet the aerial perspective, what it does, but I kind of took what I wanted from the advice you gave, and luckily, when I looked up aerial perspective, I found the answer in the mental ray section;-)

I am thinking of trying out participating media for a still though, with volume lights through the windows, but I have been rendering for the last week, so I definately won´t take more time rendering the 100 frame animation on volume ligths, he he.

Now, my new problem is the render layers and comp. It looks good with the beauty layer only, but the sky disappears in fusion, this must really be a newbie problem and easy fix, I still need to find out how though...

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