Understanding Object Views and Projection Systems in Technical Drawing
Understanding the Views of an Object
The main view of an object is obtained through orthogonal projections onto six planes arranged in a cube. We can define views as the orthogonal projections of an object according to the different directions from which it is observed.
Title of the Views
If we place an observer according to the six directions indicated by the arrows, we obtain six possible views of an object:
- View A: Front view or elevation
- View B: Top view or plan
- View C: Right side view or right lateral view
- View D: Left side view or left lateral view
- View E: Bottom view
- View F: Rear view
Relative Positions of the Views
For the arrangement of different views on paper, two orthogonal projection variants of equal importance can be used:
- The method of projection of the first dihedral, also called European (ISO E)
- The method of projection of the third dihedral, also called American (ISO A)
European System (ISO E)
Used in almost every country in the world, this system is based on the projections of the body being made on the first dihedral. The planes are considered opaque. The elements constituting the projection are the source, the body, and the projection plane (the unit of measurement is millimeters).
American System (ISO A)
This projection is based on considering the body in the third dihedral. The planes are considered transparent. The elements of this projection are the focus, the projection plane, and the body (the unit of measurement is the inch).
Projections
Projections can be defined as the figure that results from projecting all points on the boundary of a solid, or another figure, onto a flat surface. It has three key elements:
- Center of projection
- Plane of projection
- Lines of projection
Different Types of Projections
- Conic: The center of projection has a fixed and determined position.
- Cylindrical: The center of projection is at infinity. Cylindrical projection may be:
- Orthogonal: Projecting rays form an angle of 90 degrees with the projecting plane.
- Oblique: Projecting rays form an angle other than 90 degrees with the plane of projection.
Dihedral System
The dihedral system is the precursor of all systems and has the widest field of applications, especially in industry and civil works. It is also the most widespread of all known dual-projection systems, or Monge, the first French geometer who compiled it. It is a system of orthogonal cylindrical projections; that is, only orthogonal projection is used. This type of projection is the most commonly used in technical drawing. It maintains relations of parallelism, and in those dimensions that are parallel to the axes, proportionality, true shape, and true scale also remain.
In the dihedral system, projections are made on perpendicular projection planes (horizontal and vertical planes) dividing the space into four quadrants, as shown in the figure below.