Why Truncated Projection?
Refer to the image above for this discussion. Fulldome projection from a single projector solution means that the projected pixels are limited to a fully inscribed circle on the display panel. This means that only 50% of the available pixels are used, and the resolution is limited to the vertical resolution of the projector. Truncated projection optimizes the use of a single projector by inscribing the projected circle along the horizontal of the display panel. Truncated projection typically uses over 80% of the available pixels. Modern immersive environments typically use theatrical seating, with the audience all facing forward, so fulldome projection would place images behind the audience’s heads. Truncated projection places images in the audience’s natural field of view and increases both brightness and resolution by roughly 60% over fulldome projection.
The following are some examples of immersive environments using both fulldome and truncated projection. The first shows various 200 series projector placements in a fixed dome (a planetarium with an opto-mechanical projector in place). The orange section of the dome represents the extent of the projected image. Notice that in all cases using truncated projection that the “shadow region” where there is no image on the dome is always behind the user and essentially ignored.
Below is an illustration of the GeoDome Theater using truncated projection. This configuration offers distinct advantages beyond resolution and brightness. Again, the orange on the screen represents the extent of the projected image. Notice that users near the projector are not only fully immersed horizontally (the image extends beyond their FOV); they also experience image below the horizon. This downward FOV is critical to create a sense of place. For example, landing on the planet Mars is far more believable with the ground is below you rather than 8 feet in the air! The perspective image shows the extent of the projected rays and defines where the audience can be located without casting shadows on the screen.