omino pixel blog

This plugin is available for prerelease use and feedback. (I hate to say “testing” but that too.) It’s solid enough. More info and download HERE.

As introduced in yesterday’s post, you can download my Mac command line tools, om_sphere2dome to help convert Modo spherical projection images to fulldome domemaster images.

For reference, I’ll here post the tool’s help info, so you can see its feature set more easily.

poly@omino-8999 domework: om_sphere2dome --help

om_sphere2dome

This command line tool transforms a spherically-projected
image file to a Domemaster image file (180 degree fisheye).
The source image is a 2:1 aspect ratio equirectangular
projection, as produced by Modo's spherical camera. The
center square is extracted and transformed.

See https://omino.com/pixelblog/2015/03/03/modo-for-fulldome-
part-2/

--help
Optional. Show help.

--infile=<file name>
Required. A source .png or .jpg image, 2:1 aspect ratio,
spherically projected.

--outfile=<file name>
Required. The output .png or .jpg image to write, square,
Domemaster projection.

--vflip=<yes or no>
Optional. Vertically flip the image.

--size=<number>
Optional. Size of output image.

--azimuth=<number>
Optional. Shifts view negative-left or positive-right
in degrees.

Written by david.van.brink@gmail.com, 2015. Uses Lode Vandevenne's
excellent lodepng library from http://lodev.org/lodepng/. Uses Rich
Geldreich's wonderful single-file jpeg library from https://code.google.com/
p/jpeg-compressor/. 8x8 font created by John Hall, http://overcode.yak.net/
12, no longer with us.

This post will describe a means of creating fulldome domemaster images using Modo.

What is a Domemaster?

The interchange format for digital planetarium movies is a Domemaster (or Dome Master). Since planetaria require extremely high resolution (4k at least, some are using 8k), these are often delivered as a hard disk full of individual, numbered PNG files.

The format of each image is a disk, where the center of the image is projected to the top of the planetarium dome. Here’s a calibration image I found somewhere…

This is an “equal-azimuthal projection”; radius from the center corresponds directly to latitude. A nice attribute of this projection is that it looks quite natural even when it is flat. In this image, the audience would be facing South.

What Modo Provides

Modo’s camera has several projection modes, including “Spherical”. This renders a full sphere of imagery from a single camera point. It draws this into a projection known as “equirectangular”. You have probably seen a world map like this:

I grew up with one in the hallway. It fascinated me how Antarctica was smeared across the entire bottom edge. In this projection, latitude goes vertically from -90° South to +90° North, and longitude goes horizontally from -180° East to +180° West. To make the gridlines square, the width is generally twice the height.

I did some experiments with Modo’s spherical camera. The model is a closed sphere, with the axes labeled. Modo’s standard axes are Y-up, X-right, and Z-towards-you.

And here is Modo’s rendering, using Modo’s Spherical Projection Mode.

Things to notice:

1. The center of the render is from exactly behind the camera.
2. We only need the center square for our dome master (half the spherical scene).
3. The image is inverted (the “y” is backwards).

To address the first two, in Modo we point the camera exactly away from our center of interest, and we use the Frame Properties’ Render Region, to skip rendering parts of the scene we won’t need. The saved files will still be twice as wide needed, though.

And here is what what gets rendered!

Making the Domemaster

That’s better, but still inverted, and not a dome master. I wrote a command-line tool, which reads in a JPG or PNG spherical-projection file as Modo produces, and writes out a domemaster JPG or PNG file. You use it like so, from a terminal session:

poly@omino-8999 domework: om_sphere2dome --infile=sphereImage1.jpg --outfile=dome.jpg
infile: sphereImage1.jpg (1024 x 512)
outfile: dome.jpg (512 x 512)
writing dome.jpg...
write result: ok
poly@omino-8999 domework:

Running it on the last render, we get (“ta da!”):

This is a correctly formatted domemaster image. (Excepting that it’s only 512 pixels across, which will be singularly disappointing on a 75 foot dome screen. But you get the idea.)

As of today, the tool is in primitive form, and has limited image quality, and only for Mac OS X at the moment. But if you come across this and need it for Linux or Windows or have a feature request, or want the source code, please email me, poly@omino.com. It’s a living work. As it is, it’s just barely sufficient for my needs, and no more.

Also, just to reiterate, this is a command line tool; you’ll need to be comfortable with shell scripting to make full use of it. You might even need to chmod it after downloading. If that hasn’t warned you away…

Download om_sphere2Dome.

For Photoshop — Andrew Hazelden maintains this set of installable actions which can also do this transformation. For converting a whole Modo movie render, you’ll need to do a bit more scripting on top of it, and it will run fairly slowly… but it’s great to have options! His action set has many other tools as well.

I’ve recently been trying to use Modo to render images compatible with digital planetariums. If you want to know just about that, skip straight to Part 2.

Meanwhile, here in Part 1, I’ll give a quick introduction to planetarium video.

I remember visiting the Hayden Planetarium many times as a child, growing up in Manhattan. In the center was a queerly articulated two-headed beast. This was the sky projector, with lovingly-crafted high precision star maps to project glorious pinpoints of light onto the hemispherical theatre ceiling. Shows would be augmented with maybe a slide projector or two, or even a movie projector. The operator had a microphone, a flashlight with an arrow-shaped cutout, and not much else. Those were the days.

Now they’re all digital. Since I love digital video, this is pretty cool.

I recently had a very educational visit to the control booth of Chabot’s “Ask Jeeves Planetarium”, and their resident astronomer/projectionist Ben Burress brought me up to speed on how these newfangled contraptions work. Here’s what I learned; some of this is idiosyncratic to Chabot’s particular installation.

Harware.

• A dome is typically lit by 5 to 7 projectors, spaced around the edges and one for the top. Chabot uses 6.
• The theatre is typically driven by multiple computers in their server room, one for each projector and one for audio
• 5.1 audio.

Software.

• There are various softwares available for live shows. Chabot uses “Digital Sky 2.” This astronomy software uses a database of our galaxy and solar system, letting you fly around. The planets are wrapped in NASA textures, light from the sun is computed dynamically, you can move in time and space. They can also import assets (like the International Space Station, for example) to add to a particular show.
• Playback of “tiled/encoded” pre rendered content. Recorded playback consists of a movie for each projector, played back with perfect frame synchronization.
• There is a small but growing body of other softwares, including VJ tools and the like, for domes, too.

Content.

Chabot supports several kinds of content, both live and recorded (not sure how similar other theaters would be).

• Live Digital Sky 2 shows. A combination of preprogrammed cue points and assets (specific camera positions in time and space), and live control, to perform a typically 10-40 minute presentation. Takes two people to perform, usually, one to operate the dome & software, and one to narrate.
• Automated Digital Sky 2 shows. An automated recording of the control operations and narrations from a live show. Files are compact, as it only has control messages.
• Recorded Digital Sky 2 shows. Like an automated show, but it has been rendered out to video files. These files are huge. Ben said they do this a) to share a show with another theatre (who may not use Digital Sky 2), and b) they found that certain huge high-polygon assets, like a topographical Earth model, sometimes crashed when performed live.
• Automated laser music shows (like Pink Floyd). They have additionally a laser projector (not Laseriumâ„¢, some other maker) which can play back recorded, synchronized control sequences
• Recorded movie files. This is my main interest, some details of which will be covered in Part 2.

Content Creation.

The Ecosystem of dome video involves several pieces.

• A Dome Geometry File. This is a calibration file for a specific theatre describing the geometry, color balance, and brightness for the several video projectors (generally from 5 to 7) which span the dome surface.
• Dome Master content movies. A content creator generates a Dome Master which looks like a square movie with content within a central disk. The disk maps elevation-angle to radial distance. These are often shipped on a hard drive, with numbered 4096×4096 PNG files, like MyPlanetariumShow_12345.png. Audio is typically a Dolby 5.1 AC3 file.
• Nonrealtime processing. The geometry file is used to “tile” the Dome Master to separate movie files (MPEG? not sure), which are ready for playback on each projector.
• Realtime Digital Sky 2. Their astronomical software can run on all the projection computers simultaneously, and do live tiling based on the geometry files.
• Not available at Chabot: Realtime Dome Master tiling. Some theaters are equipped to take HDMI 2k or 4k input, and do live tiling based on the geometry file. This is used by VJ’s. Chabot doesn’t have this, currently.