Making of a Planet (version 0.2b) - Part 1

As promised, I shall attempt to summarize the techniques I used to create the CG Earth from the previous post. This version represents another milestone in my efforts to create a decent photorealistic Earth using computer graphics.

Before I begin, it seems more and more people are interested in Earth observation. One emerging hobby is for people to build and launch home-made high altitude balloons containing low-cost GPS systems and digital cameras up into the stratosphere to capture videos and photos of the Earth from "space". These balloon capture amazing imagery of the Earth from altitudes upwards of 30km, but is still well within the Kármán line (altitude of 100km) commonly considered the boundary between Earth's atmosphere and outer space. For comparison, the International Space Station (ISS) orbits between 278-460km above ground. Still, the balloon footage are a great source of additional reference material ^_^

Scene Setup

Okay, back to the production report. In this first post I will outline the features I have built into my scene setup and the type of options they offer for creating Earth renders.

Houdini scene

Looking at the scene network above, you can see that I have not only created the Earth, but also the Moon, Sun and the ISS. I've been careful to scale all the objects as well as their orbits to relatively accurate proportions using data from the internet. In reality, all orbits should be elliptical, but circular orbits are easier to setup for now. However, I did apply correct inclination and axial tilt parameters for both the Earth and Moon.

The Sun is 1,380,000 km across in diameter (about 110 times that of Earth), and 149,600,000km from Earth. It takes light 8.32 minutes to reach Earth from the Sun! The Earth is way much smaller than 1 pixel at this scale ^^;;

The Moon looks tiny bacause it is 384400 km away from Earth. It takes light 1.3 seconds to reach Earth from the Moon! We can make the Moon appear bigger in shot by increasing the focal length

The setup is basic CG101: just use null objects and correct parenting. So, the Earth rotates about it's axis, the ISS and Moon rotates around the Earth, and the Earth-Moon system rotates about the Sun. The animation controls are set up for properly relative orbital periods - i.e. Earth rotates on it's own axis once a day, ISS makes one revolution round the Earth in 90 minutes, Moon revolves round the Earth every 27.3 days, Earth goes round the Sun in 365.25 days. Of course, time can be allowed to speed up, slow down or stop in the CG world. Offset controls allow independent control over exactly where to position the objects in orbit to allow fine tuning for shot composition.

Cameras and Animation Controls

All this trouble to be "realistic" actually makes setting up cameras and shot composition even more difficult. So I took a more sensible approach by setting up orbital cameras around the Earth (attached to the ISS) and Moon, with controls to adjust their location and orientation. Again, it's all null objects and parenting, with expressions to drive rotation channels to simulate orbit.

Although properly set up, I ended up using this only for reference and using Maya to render the ISS because it was too much work to surface the model properly in Houdini. It was tedious in Maya too, but the workflow is much less painful.

Centering the Earth Cam on any location is as easy as entering their latitude and longitude. Here's London at 51.5171° N, 0.1062° W

View from the Moon ^^

In the next post, I'll describe how the Earth is constructed. Until then... ^^/