What does projection mean in mathematics?

[Edit this paragraph] 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 orthographic projection of point P on line A (referred to as projection). [Edit this paragraph] 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. [Edit this paragraph] Definition 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. [Edit this paragraph] The unit vector E of vector projection is 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, then the modulus of vector A' B. vector A'B' is ∣ A' B' ∣ = ∣ AB ∣ ∣. 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.