If straight lines are drawn from various points on the contour of an object to meet a plane, the object is said to be projected on that plane and the picture formed by joining these projected lines at the plane is called the projected drawing. In architectural drawing four methods of projection are commonly used.
The factor that determines which category a drawing fits into is the relationship of the objects surfaces to the viewer or the picture plane. A Picture Plane is an imaginary film placed between the viewer and the object. One can think of the picture plane as the media on which the drawing will be placed or the film in a camera onto which the image is projected.
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