cad-bim-file-conversion

CAD / BIM File Conversion

Use this when the user provides a real-estate/architectural download link or asks for files to be converted between CAD/BIM formats such as DXF, DWG, RVT, IFC, SKP, PDF floorplans, or SketchUp-compatible deliverables.

Workflow

1. Download everything first. - Use the browser if the link is a download center with buttons/forms. - Also inspect visible direct links; providers sometimes expose CDN URLs. - Preserve originals in a task output directory.

2. Do not trust displayed file extensions or CDN suffixes. - Real estate delivery platforms may show every file as .pdf even when the bytes are DXF, DWG, RVT, etc. - Always run file or equivalent magic-byte detection after download. - Rename/copy files to their real extensions before processing.

3. Choose the conversion path by source format. - RVT → IFC / RVT → browser preview: Best done with Revit/Autodesk tooling. On Linux, treat clean RVT export or full RVT tessellation as unavailable unless a converter/service is installed. If the user compares against Autodesk Viewer and expects windows, doors, families, materials, category tree, and Autodesk-like navigation, do not substitute DXF/IFC fallback geometry and call it equivalent. Preserve/upload the RVT as source-of-truth and route the real fidelity path through Autodesk Platform Services (APS/Forge) model translation + Autodesk Viewer, or an actual Revit export pipeline. For app integration details, use references/aps-rvt-autodesk-viewer.md. - DWG → IFC: Requires DWG-capable tooling (ODA/AutoCAD/FreeCAD stack if available). Verify geometry after conversion. - DXF floorplan → IFC: Can produce a usable IFC from linework with ezdxf + ifcopenshell by creating IFC4 wall/proxy geometry from polylines/lines. - DXF/IFC linework → SketchUp import: If the user asks for .skp but no real SketchUp writer is available, generate a SketchUp-importable Collada .dae from centered/extruded linework and optionally package it as .kmz; see references/sketchup-importable-dae-kmz.md. - PDF floorplan → IFC: Use only as visual/reference input unless OCR/vector extraction is explicitly needed; prefer CAD sources when present.

4. For a Linux DXF → IFC fallback: - Install/use Python packages ezdxf and ifcopenshell if available. - Read modelspace linework/polylines. - Detect units via $INSUNITS; common DXF unit code 4 is millimeters. - Center coordinates near origin to avoid huge-world-coordinate import issues. - Convert mm to m when creating IFC SI geometry. - Create an IFC4 project/site/building/storey hierarchy. - Extrude linework as thin wall geometry using ifcopenshell.api.geometry.create_2pt_wall or create proxy/mesh geometry when walls are inappropriate.

5. Verify before sending. - Re-open the generated IFC with ifcopenshell.open. - Report schema and object counts. - Send the converted file directly, plus a concise caveat about fidelity if the source was only DXF linework.

6. If the task expands into a browser BIM review app: - Use the pattern in references/browser-bim-review-studio.md. - Parse IFC metadata server-side and expose schema/entity counts in the project library. - Do not ship fake/count-driven 3D as if it were model geometry. If real geometry is not ready, show an honest placeholder plus source/download actions. - For a real browser preview, generate/load GLB: renderable IFC via ifcopenshell.geom → trimesh → GLB, or DXF linework via ezdxf extruded segments → trimesh → GLB. Verify the browser visibly loads real geometry before calling it done. - If the source is RVT and the user wants the Autodesk Viewer experience, the class of solution changes: implement APS/Autodesk Viewer (OAuth/token service, OSS upload, model derivative translation, URN loading) rather than improving a Three.js fallback. Three.js OrbitControls can improve navigation for GLB/DXF previews, but it does not recover missing Revit semantics.

User-facing handoff style

Keep the reply compact:

• State that the file is done.
• Attach the IFC file via MEDIA:/absolute/path/file.ifc.
• Include one clear caveat if it is a fallback conversion rather than a native RVT/DWG export.
• Mention where originals were saved only if useful.

Pitfalls

• Do not claim a clean BIM export from RVT unless Revit/Autodesk/IFC exporter actually ran and was verified.
• Do not present a DXF-derived GLB, IFC fallback, or simplified mesh preview as equivalent to Autodesk Viewer opening the native RVT. If Autodesk Viewer shows windows/families/elements that the app preview lacks, acknowledge the fidelity gap immediately and switch to an APS/Revit translation plan.
• Do not claim a native .skp unless SketchUp desktop or an actual SketchUp SDK writer ran and the output was verified. On Linux, prefer honest SketchUp-importable .dae/.kmz fallbacks.
• Do not rely on the filename shown by a download portal; confirm the file type by bytes.
• Avoid sending huge zip bundles unless the user asked for originals; IFC alone is usually the useful output for SketchUp.
• Preserve originals so the user can later hand them to a Revit/AutoCAD operator if a higher-fidelity export is needed.

References

• references/aryeo-cad-download-center.md — provider quirk: Aryeo/CDN files may be served with .pdf URLs while containing DXF/DWG/RVT bytes, plus a proven DXF-to-IFC fallback pattern.
• references/sketchup-importable-dae-kmz.md — fallback pattern for producing SketchUp-importable .dae/.kmz handoffs when native .skp export is unavailable.
• references/browser-bim-review-studio.md — pattern for lightweight authenticated CAD/BIM upload + IFC metadata + browser preview portals, including the placeholder-vs-true-geometry caveat.
• references/aps-rvt-autodesk-viewer.md — production pattern for RVT → Autodesk OSS/Model Derivative SVF2 → Autodesk Viewer integration in a browser app.