Convertir un plan papier ou un dessin MEP ancien en DWG/DXF propre et entièrement éditable ne doit pas donner l'impression de tout reconstruire. The goal is editability: joined polylines, true arcs, reusable blocks, searchable text. This guide gives a reproducible workflow from scan to QA.
Étape 1 — Scanner pour l'éditabilité
Target 300–600 DPI for architectural/MEP sheets. Prefer TIFF or PNG; avoid JPEG for masters. Flatten sheets, confirm orientation, include a known dimension or scale bar.
Étape 2 — Prétraiter l'image
Deskew, denoise, binarize (global or adaptive threshold). Use morphology to reconnect breaks. Test on a small region first.
Étape 3 — Vectoriser avec des réglages « éditabilité d'abord »
Balance detection thresholds, corner sensitivity, smoothing, gap-closing. Enable OCR for notes/dimensions. Define blocks for repeated symbols after conversion.
Étape 4 — Calibrer l'échelle et les unités dans le CAD
Set units (-DWGUNITS/INSUNITS). Calibrate with a known dimension (SCALE Reference or ALIGN). Verify with DIST.
Étape 5 — Nettoyage et QA
AUDIT; PURGE; OVERKILL. PEDIT Join; rebuild symbols as blocks; clean layers (LAYMRG). QA: closed polylines, real arcs, selectable text, correct scale/units.
Étape 6 — Débit et reproductibilité
Define presets per drawing type; log parameters per batch; use batch convert and named profiles where supported.
Exemple pratique — JPG/PNG vers CAD en ligne
Use Image to CAD: upload JPG/PNG, technical-drawing preset, enable OCR, export DWG/DXF. Keep 300–600 DPI; spot-check before full batch.
Dépannage — symptômes et corrections
| Symptom | Cause | Fix |
|---|---|---|
| Polylignes fragmentées | Low DPI; gap closing; noise | Rescan 300–600 DPI; denoise; PEDIT Join |
| Courbes en escalier | Low res; threshold; smoothing | Higher DPI; adaptive threshold; smoothing |
| Lignes fantômes | Shadows; JPEG artifacts | Rescan flat; avoid JPEG; deskew |
| Texte mal reconnu | Low contrast; OCR bounds | Contrast; widen OCR; correct post-export |
| Dérive d'échelle | DPI unknown; unit mismatch | -DWGUNITS; SCALE Ref or ALIGN; verify |
Quand redessiner partiellement
If scans are badly smudged or low-res, convert what you can and redraw illegible details. Hatches are often faster to reapply in CAD.
Conclusion
Scan cleanly, preprocess, vectorize with editability-first settings, lock units/scale, then cleanup and QA. Use Image to CAD to verify DPI and OCR before finalizing in your CAD.