hardware | software

Hardware: General Architecture | Alignment and Masking | Rigging lasers | Computer-controlled lasers
Software: The choice of LithTech | 2D input ->3D world | Iterations on interactivity | Implementing a storyline

Masking

This webpage will hopefully describe the challenges of (and solutions to) creating good alignment and masking in the Earth Theater. Fortunately, we need not start from scratch, since there have been many prior projects in the Earth Theater. If you are not already familiar with the basic issues of masking and alignment in the Earth Theater, please read the document created by Cort Stratton here or a copy of it here. The main points of that document are:

  • There is significant projector overlap in the Earth Theater
  • The severity of the overlap depends on the colors in the overlap region
  • The projectors and bulbs are slightly different and make the overlap more noticable
  • Only a portion (a sub-rectangle) of the video output is actually projected
  • There may be a way to automate the mask-creation process
I would add the following points:
  • The Earth Theater is a public venue that we don't have control over; settings can change in your absence.
  • There are external controls (Extron Boxes) that effect the horizontal alignment of each projector in addition to all the other controls.
  • Since the physical screens are actually a section of a sphere (and thus curved horizonally and vertically), the overlap is greatest at the top of the screen, and least at the bottom of the screen.
  • Changing the video card of the computer apparently changes the alignment of the projection as well.
  • An automated process would be great, but it would be extremely difficult to automate the creation of finely tuned masks. Overall time spent would probably be less via manual alignment and iteration.
This Earth Theater project used LithTech as the 3D engine. Therefore, the format of the HUD (Heads Up Display) must be in DTX format. Fortunately, there is a plugin for Photoshop that allows easy import and export of DTX files, to a maximum size of 1024 x 1024. Download the plugin here. You may also need two DLLs to use the DTX, which you can download here and here.

Projector Alignment

Proper projector alignment is crucial if you want the audience to be immersed in your show. Unfortunately, without spherical correction, it's impossible to get perfect alignment. You will be forced to choose a section of the screen that is nicely aligned. If you align the tops of all 5 screens, then the bottoms will be out of alignment. If you align the bottoms, then the tops will be out of alignment. For our project, we chose to align the middle of the screen; most of our content was concentrated there, and not at the very top or the very bottom. It's important for everyone on the team to be aware of the alignment issues from the beginning.

There are several different ways to align the projectors:

  1. Physically move the projectors
  2. Change the settings in the projector alignment via remote control
  3. Change the settings of the Extron boxes
  4. Change the settings in software
  5. Change the video card of the computer
If you have any questions or comments, please feel free to contact Ira Fay.