Technical Drawing Systems and Projection Methods

Dihedral System

A representation system using cylindrical projection angles.

Elements

• Two perpendicular planes of projection: Vertical plane and horizontal plane.
• Intersection: The line between the vertical and horizontal planes.

Objects can be represented as points, straight lines, or solid plane figures. Their projections are called:

• Elevation (Front view)
• Plan (Top view)
• Profile (Side view)

Dimensioning Standards

Normalization is a set of graphic rules with the objective of facilitating international comprehension of technical drawings. Dimensioning marks the measurements of a piece using lines and numbers.

Bounding Elements

• Dimension lines
• Auxiliary or reference lines
• Dimension numbers

Dimensioning Systems

• Parallel
• Series
• Combined

Detailed Drafts

Freehand drawing of a piece, done in pencil without technical drawing instruments.

Axonometric System

A representation system that provides a perspective view of solids.

Cylindrical Orthogonal Projection

• Isometric: Axes are at 120°.
• Dimetric: Two angles are equal, one is unequal.
• Trimetric: All axes form unequal angles.

Oblique Cylindrical Projection

• Cavalier Perspective: X and Z axes are at 90 degrees; a reduction coefficient is applied to the Y axis.

Conical Perspective

A system of representation reflecting three-dimensional bodies on a plane as they appear to the human eye.

Elements of Conical Perspective

• Viewpoint (V)
• Picture plane (PC)
• Geometral plane (PG)
• Horizon plane (PH)
• Horizon line (HL)
• Ground line (LT)
• Receding lines (LF)
• Vanishing points (F and F')
• Main point (P)

Visual and Metric Points

• Angular visual: The space covering the outermost points of the observed object.
• Height of the viewpoint: Distance from the viewpoint to the geometral plane.
• Metric point: Located on the horizon line, it relates perspective measures to actual measurements.

Frontal Conical Perspective

In frontal conical perspective, lines of the body perpendicular to the picture plane vanish to the main point (P). These can be determined using the dihedral system.

Oblique Conical Perspective

In oblique conical perspective, lines oblique to the picture plane vanish to points other than the principal point. These can also be determined using the dihedral system.