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View Full Version : Problem replicating a simple gradient texture in Nodal



TheDAve
07-20-2007, 10:17 AM
Can any of you nodal experts help me with a problem I am having?

I'm trying to create an image of Saturn and wanted to add some atmosphere to it (I know it may not be astromically correct, but it looks wrong without it to me:)). So I thought I'd follow the tutorial here (http://personal.southern.edu/~dascott/tutorial01/nasa-earth.htm), but just change the colours at the end.

So I followed the tutorial and ended up with this...

http://www.digitaljoat.com/Temp/1tm.jpg (http://www.digitaljoat.com/Temp/1.jpg)

Using the gradients

http://www.digitaljoat.com/Temp/3tm.jpg (http://www.digitaljoat.com/Temp/3.jpg)http://www.digitaljoat.com/Temp/4tm.jpg (http://www.digitaljoat.com/Temp/4.jpg)


Superb, I have a nice blue atmosphere in the FPrime and F9 render.

So I thought I would replicate this in Nodal, and use the colour tool node to change the hue.

Using 2 gradients setup the same (I thought - as shown) I saw this

http://www.digitaljoat.com/Temp/2tm.jpg (http://www.digitaljoat.com/Temp/2.jpg)

i.e. No atmosphere at all.


So I tried to recreate the original setup using layer nodes (again shown), this time the result was even more wrong.

http://www.digitaljoat.com/Temp/5tm.jpg (http://www.digitaljoat.com/Temp/5.jpg)

Can anyone tell me where I have made a (probably simple) mistake?

Cheers

DAve

Weepul
07-20-2007, 02:26 PM
Not sure what's up when you tried layer nodes, but it looks like the transparency gradient really went crazy...somehow. :p

As for what you were doing wrong with the Nodal gradient attempt, you set it to go from 0 to 90. In Nodal, incidence angles go from 0 to 1 (the cosine of the angle). Set it up at that scale and it should work. Funny little tidbit: I'm pretty sure the old Layer system also used the cosine of the incidence angle, but then re-scaled it to 0-90 to make you THINK it was just the angle. 8~

TheDAve
07-23-2007, 06:41 AM
Cheers weepul, I'll give that a go.

I assume I'll have to actually calculate the cosine and not just scale 0->90 to 0->1. As cosine 45 degrees == 0.7 not 0.5.

Cheers,

DAve

starbase1
07-23-2007, 08:56 AM
I'm trying to create an image of Saturn and wanted to add some atmosphere to it (I know it may not be astromically correct, but it looks wrong without it to me:)). Cheers

DAve

A fuzzy edge is indeed wrong, but there are plenty of Cassini images that show the limb shading towards a pale blue colour.

Here's one I did recently:
http://www.starbase1.co.uk/galleries/Recent%20Images/slides/mimas-extreme.html

For accuracy, the subtle blue should be a lot stronger on the limb where the ring shadow falls. I started with something similar to you (non nodal), and lowered the height of the armosphere layer until it was barely above the planet at all. (well under 1 pixel).

See here for a seriously dramatic NASA image:
http://science.nasa.gov/headlines/y2005/17feb_bluesaturn.htm

Scazzino
07-23-2007, 01:30 PM
Here's a Saturn scene (http://dreamlight.com/insights/12/3DSetsAndProps.html#spaceset) I did a while ago with only gradients.

It's based on this Hubble image (http://hubblesite.org/newscenter/archive/releases/2003/23/image/c/format/large_web).

TheDAve
07-23-2007, 04:40 PM
Oddly enough Nick, you were the one i was thinking about with the "not be astromically correct" comment :)

Well I tried changing the degree's to cos(degree's) and did not have much more luck. I can see I'm going to have to sit down and have a good think about this. But since the non-nodal texture layers give me roughly what I need this may sit on the back burner for a while.

Thanks for the help.

DAve

Weepul
07-24-2007, 08:43 PM
Cheers weepul, I'll give that a go.

I assume I'll have to actually calculate the cosine and not just scale 0->90 to 0->1. As cosine 45 degrees == 0.7 not 0.5.
Not really. That's why I mentioned that I was pretty sure that the old way of doing it was not actually degrees, but the cosine just scaled up to be 0-90. ;) 45 should equal 0.5 in Nodal.

TheDAve
07-27-2007, 07:32 AM
Ah that would explain my last failure.

:)

DAve