Chapter 10: Plans and Elevations

Chapter 10: Plans and Elevations

21.1 : Orthogonal Projections*Identifying orthogonal projections

The orthogonal projection of an object on a plane is the image (shadow) formedby the normal from the object onto the plane.

If the projection lines are not normal to the horizontal plane, then the image formed onto the plane is not the orthogonal projection of the object.

Example 1For each of the following, state whether the projection onto the plane ABCD parallel to the shaded surface is the orthogonal projection for the object given.

*Drawing orthogonal projectionsTo draw the orthogonal projection of a given object on a plane :(a) Draw the normals from each verticles of the object to the given plane.(b) Join all the points on the plane.