Model for Descriptive Geometry by A. Jullien - Angle between a Line and a Plane

Jullien, A. · ca 1880

The given plane is CPC’ and the line goes from b on the horizontal plane to a’ on the vertical plane. The holes can be seen in the image, but the black string is missing. Point (m, m’) is any point on the line. Construct the line from (m, m’) to point d on the horizontal plane that is perpendicular to the plane. This line is the wire protruding out of the horizontal plane. Through the use of several projections seen in the relief, point M₂ on the horizontal plane is the image of the rotation of point (m, m’). Then angle fM₂d on the horizontal plane is the angle between the given plane and line.