Terminology used in Perspective Projection

TERMINOLOGY USED IN PERSPECTIVE PROJECTION

The important terms generally used in perspective projection are shown in Fig. 18.6. and are explained below.

1. Ground plane (GP): A horizontal plane on which the object is assumed to be placed is known as Ground plane. The observer also stands on this plane from a convenient distance to view the object. 

2. Horizon Plane (HP): It is an imaginary plane in horizontal position, parallel to the ground plane and passing through the observer's eye (or) the station point.

3. Auxiliary Ground Plane (AGP): It is also an imaginary plane in horizontal position, parallel to the ground plane and placed above the horizon plane. This plane is used to draw the top view of the perspective rays and the object (Not shown in Fig.18.6.)

4. Station Point (SP): The position of the observer's eye from where the object is viewed is known as station point.

5. Picture Plane (PP): It is a transparent vertical plane placed in between the observer (ie. station point) and the object. The perspective view of an object is drawn on this picture plane.

6. Central Plane (CP): It is an imaginary vertical plane perpendicular to both the ground plane and the picture plane which passes through the station point.

7. Ground Line (GL): It is the line of intersection of the ground plane with the picture plane. 

8. Auxiliary Ground Line (AGL): It is the line of intersection of the picture plane with the auxiliary ground plane (not shown in Fig. 18.6).

9. Horizon Line (HL): It is the line of intersection of the picture plane with the horizon plane. Horizon line is parallel to Ground line.

10. Centre Line (CL): It is the line of intersection of the picture plane with the central plane. 

11. Axis of Vision (AV): It is the line drawn perpendicular to the picture plane and passing through the station point. It is also called as the line of sight, central ray, axis of sight, perpendicular axis (or) Principal visual ray.

12. Centre of Vision (CV): It is the point of intersection of the axis of vision with the horizon line.

13. Visual Rays (VR): These are the imaginary lines joining the different points on the object to the station point. 

14. Vanishing Point: The visual rays which converge at a point on the horizon line is known as vanishing point.

15. Horizontal distance: The distance between the station point and the picture plane is generally known as Horizontal distance.