Ok, here's a small tutorial for the double helix.

I attached an early version of the tgd, which doesn't contain a helix, but it shows the basics of the method of displacement.

There's also a screenshot of the network from the final version.

I took the following steps to create the double helix:

- make a simple pillar

- use displacement to turn it into a helix

- combine two helices into one double helix

For the pillar, I used a simple cone. I don't want to go into the details, because I think that's not the interesting part of this network.

__Creating a helix/spiral__I used displacement and redirects to achieve the shape I wanted. You can see, there are some trigonometric functions. If you take a look at the wikipedia page for "Helix", you'll find the following way to define a helix in three-dimensional space:

x = cos(t)

y = sin(t)

z = t

Before we look into the use of this definition in TG2, lets try and understand why this definition actually works.

I attached a picture of a phone cord, shot from the side. As you can see, it follows the sine function. This is represented by the line "y = sin(t)"

Now.. if we rotate the cord by 90°, it is still a sine function, but it's shifted by 90°, which is cosine.

Now we need to adjust the definition. First of all, we simplify it to

x = cos(z)

y = sin(z)

We also have to fit it into the coordinate system of TG2, where Y is the altitude and the values of X and Z depend on the altitude:

X = cos(Y)

Z = sin(Y)

We use displacement to represent functions in TG2, but displacement doesn't work exactly in our desired directions.

A simple redirect solves the problems - it allows us to displace the pillar in X and Z-direction.

That's it.

__Combination__Now we build another helix (copy/paste) with some minor adjustments: It's z-value has to be added with pi, so the two helices aren't congruent but twist around each other.

I just couldn't figure out, how to do combine the two sprials with shaders, so I used another planet, identical to the already existing one and placed the second helix there. Because both planets are at exactly the same position, the two spirals grow at the same place and form a double helix.