Descriptive Geometry Engineers (and others)often use two- dimensional pictures to communicate three-dimensional shapes.The most common way to represent a three- dimensional object in a two-dimensional plane is by orthogonal projection. Shanghai Jiao Tong University 5Shanghai Jiao Tong University 5 Descriptive Geometry n Engineers (and others) often use two- dimensional pictures to communicate three-dimensional shapes. The most common way to represent a three- dimensional object in a two-dimensional plane is by orthogonal projection