Characteristics of projection: 1. The size of the projection varies with the distance from the projection plane of the object. 2. Characteristics of parallel projection method: When the space object moves in parallel in the projection system, the projection shape and projection center move to infinity, and the projection lines are flush with each other. The role of projection: in life, the use of projectors is mainly reflected in audio-visual entertainment. You can watch live and on-demand online. After connecting the microphone, you can enjoy karaoke at home. The projector can also be turned into a speaker to play mobile phone music independently. In addition, more and more people began to take projection photos of online celebrities. In the educational business scene, projectors are frequently used, and multimedia education forms are becoming more and more common.