Hue’s Beginner’s Guide to Fulldome

This tutorial is intended to be a beginner friendly no-frills guide to creating content for Digital Fulldome Theaters. We New Mexico dome folk have had a lot of interest from students and independent artists wanting to make content for DomeFest and other fulldome festivals as well as for UNM and ARTS Lab student work. This guide will help to explain the basics of the process. See also our tutorials for making a hemi-cubic 5 camera rig including files for Autodesk Maya and Adobe After Effects.

There are two main flavors of playback systems for fulldome presentation, “real time” and “pre-rendered.” Real time systems can be compared to game engines, in that they project 3D models and a camera POV in real time. A real time fulldome system can then take a still image, a 3D file, and/or a small movie file and display it with instructions to move, reposition, rotate or resize on the fly, similar to the old familiar multiple slide projector shows in older planetaria. The Real Time system takes the material and slices it up and distributes it to the appropriate projectors on the fly. (The system also encompasses a very sophisticated database for display of astronomical material. Quite an accomplishment!)  If you want to use the Realtime method, you will need to determine if the dome you are producing for has such a system, and then you will need to gain access to instructions for scripting for that system. (our gDome uses Sky-Skan’s Digital Sky.)

The brilliant graphics folks here at ARTS Lab, working on a grant which also includes the great minds at the Santa Fe Complex and the American Institute of Indian Art, are having promising success developing a new real time system using a single computer with multiple graphics cards, GPU processing, and OpenGL to create an interactive user interface for the dome. (I get to call them brilliant as I am their doting pseudo granny…;-) Running several student built scientific models and game environments, we hope to further the ability to build interactive fully immersive environments to support the future of entertainment as well as education, research, data visualization, health and medical applications and anything else our creative desendents can dream up.

The other flavor of fulldome projection is often called “pre-rendered playback” and can be compared to movie or video playback. This second type of playback requires a 30 frames per second sequence of large format images called “dome masters.” This tutorial will explain “dome masters” and the basics of how to make them. (Please refer to individual festivals’ and venues’ sites for specs on exactly how to make your dome masters for any specific event or venue. They may have very detailed instructions for size, format, naming, etc. as well as specs for sound files, although this aspect of fulldome production has loosened up considerably since we began, allowing for a wider variety of formats and forms.)

What’s a Dome Master?

The image to the right is a “dome master.” Notice that it is a circular image within a square. The outer edge of the circle corresponds with the lower edge or “springline” of the dome. (In this view, the bottom of the dome master is the front of the dome. Some domes may request that dome masters be configured differently, such as flipped horizontally. This example has text in the corner so the dome personnel doing the slicing can determine what you want.) The black corners will usually be discarded by the dome’s display system. Fulldome playback will generally require 30 dome masters per second of playback time.

Beginners to dome production are most often confused by the multiple projectors, and the belief that they must be concerned with what goes to which projector. All you need to worry about is the dome masters. The dome’s projector system will worry about the projectors. Each domed theater is custom built and they may have a different number of projectors placed at slightly different angles. The system is configured to take the dome masters and process them to their individual specifications. Your dome masters will be “sliced” into the correct number and shape of pieces for the projectors, and you don’t have to have anything to do with that! The dome masters are the common ground between the various domes.

(Note: the one exception is that domes may be tilted to different angles… which places the apparent horizon line or “concept of level” differently, especially in a completely horizontal or vertical dome… so you may need to make dome masters designed for a particular tilt if you need the appearance of a level horizon. Note that the dome master above has a bit of earth visible along the lower edge of the circle (the front,) while the buidings at the top (back) are cut off at the bottom. This is due to a -20% tilt in the production of the dome master to compensate for the tilt of the dome. Some stitching software will allow you to adjust the tilt so you don’t have to re-render your dome masters for a differently tilted dome, but you need to plan ahead and render more than a 180 degree view to accomodate. In the case of a hemi-cubic camera this simply means rendering the entire F, B, L, R camera frames rather than just the top half. Don’t worry, this statement will make sense after you read the hemi-cubic camera tutorial, in which you are shown how to render only the top half of the front, back, left and right views.) If you are using some sort of a fish eye solution, this will require rendering more degrees of the view.

Dome masters can be created in a 2D fashion or in a 3D fashion. The first pair of images are a tree photo which has been mirrored on both the x and y axis in a 2D After Effects comp, creating a kaleidoscopic effect. This is an appropriate way to deal with material which will not suffer from a bit of distortion, and which does not need to create a sense of realistic space. (But due to how the system distorts the dome master to fit the projections, if you were to place a video of a dancer along the edge of a 2D dome master, for instance, the human form would appear squished horizontally by about a third when projected onto the dome.)

The second pair of images were created in a 3D world, and will properly create a realistic 3D space in the dome. This is done by placing objects in 3D space around a camera rig specially designed to create a dome master. (See my other tutorials on virtual hemi-cubic camera setups.) Notice how the green torus and the red cylinder in the dome master are half again wider horizontally than when they are projected onto the dome. Almost all of the distortion in the dome master occurs out near the edges and in a horizontal direction. Also notice that although the tree kaleidoscope has the same distortion, it is not especially noticeable with this sort of image.

In the following two images, you see a hemi-sphere, and a flat disk. Basic middle school geometry will tell you that the two yellow lines in the first image are exactly the same measure, while the two lines in the second image are different by a factor of approximately 1:1.5. In other words, the line across the middle is about two-thirds the length of the line along the edge. The distortion required to make a dome master look correct when projected onto a domed surface is governed by these proportions. There is very little distortion at the center of the dome master and there is little or no vertical distortion moving out from the center to the edge. But there is a 1.5 to 1 horizontal squeeze ratio along the horizon or “springline.”(And of course this grows proportionally from 1:1 at the center to 1:1.5 at the edge, according to the math governing a “polar projection.” A classic full 180 degree fisheye distortion will create a proper dome master.)

So, why can’t I just put a fisheye lens on my video camera and shoot full video dome masters?

Why can’t you just put a frame of fisheye video on the dome?

Well, on some very small personal domes, you can. But for most domes designed to hold more than 2 or 3 people, especially fulldome theaters designed to hold a full audience, the domed screen simply requires a lot more pixels than a video camera can create, even more than a hi-def camera can create, in a single framed shot. Usually anything from 3K to 8K (and growing!)

The image to the right shows the relative sizes of a 3200 x 3200 dome master, a standard frame of video and a frame of high definition video. You can clearly see that even the full 1080 hi-def frame is less than one third as big as it needs to be for even a 3K dome master.

Often, the first thought is to try to stitch several video images together. Just remember that there is also a drop off in color at the edges of a frame of video. So you will not get a seamless image by simply butting video frames together.

There are a lot of people working on ways tocreate a dome master with multiple cameras, including some quite interesting lo tech and home-built solutions. And a lot of folks are also playing around with hiRes stills and stop motion, as well as giga-pixel technologies. Some interesting work is being made out there!

Also, there are folks creating fulldome materials using computational methods, several apps kluged together in very creative ways, hand drawings, multiple unstitched projections, fulldome production has really taken off in the last 5 years, and the number of fascinating student works we see each year promises a very interesting future!

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