What does it mean that some competing systems have truncated projection?
Systems with a truncated projection do not project over a full hemispherical dome — some portions of the sky are not projected. Usually truncation is a tradeoff to reduce costs or improve resolution in the areas that are projected. Digitarium Systems are true full-dome systems and project the entire sky with a full, uninterrupted horizon onto a dome. We feel that for astronomy education having a full sky projection is critical. The whole point of a planetarium is to immerse the audience in a full simulation of the night sky so that three dimensional concepts can be experienced first hand. Having empty black areas in the sky makes both teaching and learning in a planetarium more difficult for obvious reasons. Here is a visual comparison of approximate sky coverage for 1.) a fulldome system such as a Digitarium, 2.) a spherical mirror system with a 4:3 aspect projector, and 3.) a truncated 4:3 aspect fisheye projection system. Red areas are areas with no projection coverage.
