Projection means asking God for help.

The projection of a point on a straight line is defined as 1: the vertical foot Q obtained by drawing a vertical line from point P to line A is called the orthogonal projection of point P on line A (referred to as projection). The projective definition of a point on the plane 2: the vertical foot q obtained by drawing a vertical line from point P to plane α is called the orthogonal projection of point P on plane α. Definition of the projection of a figure on a plane 3: If the figure F' is formed by the projection of all points on the figure F on a plane, then F' is called the projection of the figure F on this plane. Practice: Case 1, the straight line is parallel to the plane, take any two points on the straight line, make the plane vertical respectively, and connect the two vertical feet in the plane. A connected straight line is the projection of a straight line on a plane. In case 2, when a straight line intersects a plane, take a point outside the plane where the straight line is located as the plane perpendicular, and connect the vertical foot with (the intersection of the straight line and the plane) to get a straight line, which is the projection of the straight line on the plane. [Edit this paragraph] Let the projection of unit vector E be the direction vector of straight line M, vector AB= a, projection A' of point A on straight line M and projection B' of point B on straight line M, and then call it vector A'B'. The note of vector A' B' ∣ a' b' ∣ = ∣ ab ∣∣ cos ∣ a, e ∣ = ∣ a e ∣. Projection is a term in geometry, and projective geometry studies the projective properties of graphs. Once, it was also called projective geometry. In classical geometry, projective geometry is in a special position, through which other geometries can be linked. Some contents of projective geometry were discovered in 2000 BC. Based on the needs of cartography and architecture, ancient Greek geometricians began to study perspective, namely projection and silhouette. But it was not until the19th century that an independent system was formed and became more complete. 1822, French mathematician Poncelet published the first systematic work on projective geometry. He was the first mathematician to realize that projective geometry is a new branch of mathematics. Projective geometry is widely used in aviation, surveying, drawing and photography.