How to protect a paper drawing archive: a practical guide to scanning and raster-to-vector conversion

Many organisations hold thousands of paper drawings, from A3 sheets to A0+ plans and maps. Together they record how facilities, buildings and infrastructure were actually built. One fire, flood or leaking roof can destroy them, and so can decades of handling. Digitising the archive protects it, and it also makes the information much easier to use.

Why paper archives are at risk

Paper archives usually decline slowly and without anyone noticing. Sheets tear along their folds. Diazo prints fade. Drawings are borrowed and never returned. Sometimes the only person who knows where a drawing is filed retires. When a drawing is finally needed for a modification, an inspection or a dispute, it may be damaged or missing.

A digital archive removes most of these risks. Scanned drawings can be copied, backed up, searched and shared without the original ever leaving storage.

Step 1: Survey and prioritise

Before any scanning begins, find out what you have:

• Volume and sizes: roughly how many sheets there are in each size, from A4 and A3 up to A0 and oversized rolls.
• Condition: fragile, torn or taped sheets need careful handling and may call for a different scanner or feed.
• Content type: black-and-white line drawings, colour maps, and marked-up or annotated prints.
• Business value: which drawings describe live assets that will be modified or inspected. Scan these first.

Step 2: Scan at the right settings

Large-format scanners such as Contex capture sheets up to 44″ and 60″ wide at unlimited length, in monochrome or colour. A few settings make a big difference to the result:

• Colour mode: monochrome or greyscale suits most line drawings and keeps files small. Use colour for maps, coloured markups and anything where colour carries meaning.
• Resolution: for engineering line drawings, 300 to 400 dpi is a common choice. Very fine detail or small text may need more.
• Clean-up: deskewing, despeckling and background removal make scans easier to read and give better results if the drawing is later converted to CAD.
• File format: multi-page TIFF or PDF are common archive formats. Agree on one standard at the start and keep to it.

Avision A3/A4 document scanners handle the smaller documents that usually sit next to the drawings, such as specifications, letters and data sheets.

Step 3: Decide what needs to become CAD

Not every drawing needs converting to vector. A scanned image is enough for reference. But drawings of assets that will be modified are worth converting to editable CAD.

• Raster editing: tools such as GTX RasterCAD and Autodesk Raster Design let you edit the scanned image directly, which is useful for quick revisions.
• Raster-to-vector conversion: GTX ImageCAD and similar tools turn raster linework into CAD entities that can be used in AutoCAD or MicroStation.
• Hybrid drawings: keeping the scan as a background underlay and redrawing only the areas that change is often the most cost-effective option.

Step 4: Index, store and retrieve

A digital archive is only useful if people can find things in it. Set naming conventions and metadata early, including drawing number, title, revision, facility and discipline. Store files in a managed location with backups. A document management system such as FileHold adds search, version control and access permissions, so the right people can find the right drawing quickly.

For storage, choose whatever suits your IT environment: a network storage location (NAS), external drives, or optical media for offline copies. For important records, keep more than one copy, in more than one place.

In-house or bureau service?

There are two ways to run a digitisation project:

1. In-house: CDSS supplies, installs and supports the scanners and software on your premises, and trains your staff to run them. This suits organisations with ongoing scanning needs or drawings that must not leave site.
2. Managed bureau service: CDSS scans, converts and archives the drawings for you, using Contex scanners, HP DesignJet plotters and GTX conversion software. This suits one-off backlogs, or teams without the capacity to do the work themselves.

CDSS Editorial Team

Engineers and specialists at CDSS (Nig.) Limited, Nigeria's first CADD technology company since 1989.