Overview
ISO 5456-3:1996 - "Technical drawings - Projection methods - Part 3: Axonometric representations" defines recommended rules and conventions for axonometric (parallel) pictorial projections used in technical drawings. It explains the geometric basis (parallel projection from an infinitely distant point onto a single projection plane), prescribes how to position coordinate axes and the object, and identifies a small set of axonometric types suitable for engineering, electrical, construction and related technical documentation.
Key topics and technical requirements
- Projection principle: Axonometric representations are parallel projections from an infinitely distant projection centre onto the drawing plane (suitable approximation for distant views).
- Coordinate system: Choose axes so the Z‑axis is vertical; projected axes on the drawing plane are labeled X, Y, Z (use uppercase for axes and lowercase x, y, z when mixing with other labels).
- Object orientation: Orient principal faces, axes and edges parallel to coordinate planes so the principal view corresponds to the orthogonal projection.
- Recommended axonometries:
- Isometric - projection plane forms equal angles with X, Y, Z; projected unit lengths equal and commonly drawn on an equilateral-triangle grid. Projected unit length ≈ sqrt(2/3) ≈ 0.816; equivalent enlargement factor ≈ sqrt(3/2) ≈ 1.225 when representing with unit lengths of 1 on the drawing.
- Dimetric - used when one view is of primary importance; projected scale ratios typically ux':uy':uz' = 1/2 : 1 : 1 (per example in the standard).
- Oblique - projection plane parallel to one coordinate plane; includes:
- Cavalier - third axis projected at 45° with same scale on all axes.
- Cabinet - similar to cavalier but third axis scaled by 1/2 to reduce distortion.
- Planometric - projection plane parallel to horizontal plane; variants include normal (scales 1:1:1) and shortened (scales 1:1:2/3).
- Drawing conventions:
- Hidden contours and edges are normally omitted.
- Axes of symmetry not drawn unless needed.
- Hatching for sections is preferably at 45° relative to axes/contours, with hatching for planes parallel to coordinate planes drawn parallel to the projected axis.
- Dimensioning: Generally avoided on axonometric views; if needed, follow ISO 129 and ISO 3098-1 rules.
Applications and practical value
- Use ISO 5456-3 for consistent pictorial representations in:
- Mechanical part and assembly illustrations
- Technical manuals and product documentation
- Architectural and construction sketches
- Town planning and map-like views (planometric axonometry)
- Technical illustrations where a clear, measurable pictorial view is required
- Benefits include predictable visual proportions, standardized scales and axis placement that improve readability, interoperability, and CAD/BIM output consistency.
Who should use this standard
- Drafters, CAD technicians, technical illustrators, mechanical and civil engineers, architects, documentation specialists, and standards authors preparing or checking technical drawings and product documentation.
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