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CAD (Computer-Aided Design) refers to the computer-based creation and editing of technical drawings and 3D models using CAD software. CAD systems represent geometry precisely, speed up planning and documentation, and form the basis for manufacturing, construction and operation.
Why is CAD important?
- Precision and consistency: Exact geometry and dimensions reduce planning errors and costly revisions.
- Efficiency: Changes can be propagated across views and plans; libraries and blocks support reuse.
- Collaboration: Data exchange via established formats such as DWG, DXF, STEP and IFC enables cross-disciplinary workflows.
- Bridge to BIM: CAD data can feed into model-based processes such as scan-to-BIM, clash detection and quantity takeoff.
How CAD works in practice
- Basis: Existing data from a digital site survey, such as point clouds, photos or scans, or specifications from the planning process.
- Modelling/drawing: 2D CAD layouts such as floor plans, sections and elevations, or 3D models with layers, blocks and parameters.
- Derivations: Automated plans, bills of materials and sections; standardised representation ensures consistency.
- Exchange: Export and import via DWG/DXF for 2D and 3D data, STEP/IGES for mechanical engineering, IFC for BIM, plus plot/PDF output for general readability.
- Quality: Naming conventions, layer standards, attribute maintenance and version management ensure reuse and traceability.
CAD vs. BIM
- CAD: Focuses on geometry and drawings, often file-based.
- BIM: Process- and information-driven, using semantic building elements, rules, attributes and a shared data environment.
Note: Modern tools often combine both approaches. What matters is a clear definition of the objective: drawing or information model.
Common mistakes and misunderstandings
- “3D = BIM”: A 3D CAD model without attributes or processes is not BIM.
- Unclear standards: Missing layers or naming conventions lead to extra work and data loss.
- Wrong export: Unsuitable formats or settings, such as missing units, slow down downstream processes.
- Media discontinuities: Manual transfers instead of direct interfaces increase the error rate.
- Isolated blocks: Libraries without metadata make quantity takeoff and operation more difficult.
File formats: selected examples
- DWG: Proprietary CAD format for 2D and 3D CAD drawings, commonly used in building construction.
- DXF: Open exchange format for 2D and 3D geometry across different software systems.
- IFC: Open standard for BIM models, including geometry and attributes.
- STL/OBJ: Triangle meshes for 3D printing and visualisation, without semantics.
- STEP/IGES: Exchange formats used in mechanical engineering and product design.
FAQ
What is the difference between CAD and BIM?
CAD focuses on geometry and drawings. BIM extends this with structured information, rules and collaborative processes across the asset lifecycle.
Which formats are suitable for data exchange?
For 2D and 3D drawings, DWG/DXF are suitable. For BIM models, IFC is used. For 3D printing and visualisation, STL/OBJ are common. For mechanical engineering, STEP/IGES are typical. Units and coordinates should always be checked.