Figure 7.18 Point view of an oblique linePlanes
A plane can be defined as a flat surface that is not curved or
warped. And a plane can be fixed in space by locating any
three points that lie in its surface and are not in a straight line.
A line and a point, two intersecting lines, or two parallel lines
also define a plane.
Classification of Planes
When a plane is parallel to a principal projection plane, it is a
principal plane. A principal plane can be a horizontal plane, a
frontal plane, or a profile plane depending on its relation ship
to a principal projection plane. All lines in a horizontal plane,
frontal plane, or profile plane are true length lines; therefore
principal planes are made up of principal lines. Principal
planes can be classified as: