Projection of Points
Theory
What is a Point?
A point represents a location in space or on a drawing. It has no width, height and depth. It is represented by the intersection of two lines. A point may be situated in any one of the four quadrants formed by the two principal panes of projection or may lie in any one or both.
What is Projection of Point?
When we drop a perpendicular from a point to a line or a plane, the point on that line or plane is called as the projection of point. The perpendicular drop is called as projector. Or the projector can be defined as the perpendicular line to xy joining the top view and the front view of a point.
What is orthographic projection?
Orthographic projection is a technical drawing in which different views of an object are projected on different reference planes observing perpendicular to respective reference plane. On opening the quadrants, HP is rotated clockwise and brought in the plane of VP. After rotation-
- Above XY line, lies the upper part of the VP and rear part of the HP
- Below XY line, lies the lower part of the VP and front part of the HP
Important Notations
| Position of the Point | Notations |
|---|---|
| Actual positions of a point | A, B, C, D, ... |
| Front view of a point | a', b', c', d', ... |
| Top view of a point | a, b, c, d, ... |
| Profile/Side view of a point | a’’, b’’, c’’, d’’, ... |
Possible Positions of the point
- In 1st Quadrant: In front of VP and above HP
- In 2nd Quadrant: Behind VP and above HP
- In 3rd Quadrant: Behind VP and below HP
- In 4th Quadrant: In front of VP and below HP
| S. No. | Position of the Point | Front View | Top View | Quadrant |
|---|---|---|---|---|
| 1. | Above HP & On VP | Above XY | On XY | First or Second |
| 2. | Below HP & On VP | Below XY | On XY | Third or Fourth |
| 3. | On HP & In front of VP | On XY | Below XY | First or Fourth |
| 4. | On HP & Behind VP | On XY | Above XY | Second or Third |
| 5. | Above HP & In front of VP | Above XY | Below XY | First |
| 6. | Above HP & Behind VP | Above XY | Above XY | Second |
| 7. | Below HP & Behind VP | Below XY | Above XY | Third |
| 8. | Below HP & In front of VP | Below XY | Below XY | Fourth |