Designing Buildings at 08:51, 9 November 2026

2026-11-09T08:51:34Z

Ali Ismailov: Created page with "Many existing buildings only have their drawings on paper: dyeline prints, old tracings, photocopies, or scans of them saved as PDF. Before an extension, a refurbishment or a cha..."

2026-11-05T13:03:18Z

Created page with "Many existing buildings only have their drawings on paper: dyeline prints, old tracings, photocopies, or scans of them saved as PDF. Before an extension, a refurbishment or a cha..."

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Many existing buildings only have their drawings on paper: dyeline prints, old tracings, photocopies, or scans of them saved as PDF. Before an extension, a refurbishment or a change of use, someone usually needs those drawings in CAD. This article sets out the common ways to do that, and where each one goes wrong.

== Vector PDF or scan? ==

The first question is what kind of file you have. A PDF exported from a CAD program holds lines, arcs and text as vectors. A scanned PDF, or a photo of a drawing, holds only pixels.

The difference matters. Since AutoCAD 2017, the PDFIMPORT command brings the geometry of a vector PDF into a drawing, often with layers and text intact. On a scanned PDF the same command can only place the page as an image, because there are no lines in the file to import. Many people meet this as the message that no objects were imported.

A quick test: zoom in a long way. If lines stay sharp, it is vector. If they break into squares, it is a scan.

== Ways to convert a scanned drawing ==

Redrawing by hand. The scan is inserted as an image, scaled, and traced over in CAD. This gives clean, editable geometry and lets the drafter make sense of faded or unclear areas. It is also slow: a detailed house plan can take a day or more.

Raster to vector tracing. Tracing software turns dark pixels into lines. It is fast and works well on clean line work, such as a simple site outline or a part profile. On architectural drawings it copies everything that is dark, including stains, fold marks, hatching and handwriting, and a wall usually comes out as two ragged outlines rather than one object. The result normally needs heavy cleaning.

AI redrawing tools. A newer group of tools reads the drawing as a plan rather than as pixels: they recognise walls, doors, windows and rooms and draw them again as CAD objects on separate layers, sometimes with a 3D model. Examples include FloorScan and Horezmi. They are quick on clear plans; on dense or damaged sheets they can misread elements, so the output should be checked against the original.

Measured survey. When the paper drawings are known to be out of date, or the building has been altered, converting them only reproduces old errors. A measured survey, by tape, laser or point cloud, gives drawings of what is actually there.

== Getting the scale right ==

A scan has no units. Scale is usually set from a dimension written on the drawing, or from the scale bar, using a command such as SCALE with the reference option. Two checks are worth making:

* set the scale from a long dimension rather than a short one, as small errors grow over distance;
* check a second dimension in the other direction, because scanners and photocopiers can stretch a sheet slightly more one way than the other.

A phone photo taken at an angle also distorts the drawing. It should be straightened before scaling, or retaken square on.

== Checking the result ==

Whichever method is used, compare the CAD drawing with the original before relying on it:

* overall dimensions and the main room sizes;
* door and window positions and counts;
* wall thicknesses, which tracing often gets wrong;
* text and room names, which tracing turns into shapes rather than editable text.

Old drawings themselves are not always right. Where the work depends on exact sizes, key dimensions should be checked on site.

== Related articles on Designing Buildings ==

* [[Types_of_drawings_for_building_design|Types of drawings for building design]]
* [[Existing_Conditions_Survey_in_Digital_Construction|Existing Conditions Survey in Digital Construction]]
* [[PDF_to_BIM_conversion|PDF to BIM conversion]]
* [[Building_archaeology|Building archaeology]]

[[Category:DCN_Guidance]] [[Category:Design]] [[Category:BIM]]

Converting paper and scanned drawings to CAD - Revision history

Designing Buildings at 08:51, 9 November 2026

Ali Ismailov: Created page with "Many existing buildings only have their drawings on paper: dyeline prints, old tracings, photocopies, or scans of them saved as PDF. Before an extension, a refurbishment or a cha..."