PDF to BIM conversion

[edit] Introduction

PDF to BIM conversion is the process of creating a building information model (BIM) from information contained in PDF drawings and other documentation. It is commonly used where the original BIM model is unavailable but existing drawings provide sufficient information to create a digital representation of a building or other built asset.

A PDF is primarily a document format and does not, in itself, contain the structured relationships and object information associated with a BIM model. PDF drawings may contain floor plans, elevations, sections, schedules, dimensions and construction details, but these generally need to be interpreted and reconstructed as model elements. The resulting model can contain both geometric and non-geometric information, depending on the requirements of the project and the information available in the source documentation.

PDF to BIM conversion can therefore form part of the process of creating or updating information models for existing buildings, particularly where documentation has been produced using traditional 2D drawing methods.

[edit] PDF to BIM process

The process varies according to the type, quality and completeness of the source information and the required level of information in the resulting model. A typical workflow begins with reviewing the available PDF drawings and establishing the information requirements for the model. This may include checking floor plans, elevations, sections, schedules, details and revisions for consistency.

The BIM project is then configured using the required units, levels, coordinates, naming conventions, object classifications and other project standards. Building elements are subsequently modelled from the available information. These may include walls, floors, roofs, doors, windows, stairs, columns, beams and building services. Where the drawings contain insufficient information, assumptions may be required, but these should be identified and recorded rather than presented as verified information.

Information can then be associated with model elements according to the project's information requirements. This may include materials, dimensions, classifications, system information and other properties. The completed model is checked against the source documentation to identify discrepancies in geometry, dimensions, alignment, positioning and other relevant information.

The quality and usefulness of the resulting model depend on the quality of the source information. A BIM model created from incomplete or inaccurate drawings cannot necessarily be considered an accurate representation of the existing building. Where greater certainty about existing conditions is required, other information sources, such as site surveys, measured surveys, laser scanning or point cloud data, may be used alongside the PDF documentation.

[edit] Applications and benefits

PDF to BIM conversion can be particularly useful for existing buildings for which the original BIM files are unavailable. Applications can include refurbishment, alteration, extension, retrofit, restoration, asset management and facilities management. It can also be used where legacy 2D documentation needs to be incorporated into a wider BIM workflow.

Creating a BIM model from existing drawings can provide a three-dimensional representation of the building and establish relationships between building elements that are not readily apparent in separate 2D drawings. Depending on the scope and information content of the model, this can support design coordination, spatial analysis, quantity take-off, documentation, refurbishment planning and facilities management.

Potential benefits include:

• improved visualisation of existing building information;
• improved coordination between architectural, structural and building services information;
• identification of potential spatial conflicts during design development;
• improved ability to extract quantities and other information from modelled elements;
• easier development and updating of project documentation;
• support for refurbishment, retrofit, alteration and extension projects; and
• creation of structured information that can be used during later stages of the asset lifecycle.

These benefits depend on the quality and completeness of the model and should not be assumed simply because the source drawings have been converted into a BIM environment.

[edit] Sources and limitations

PDF drawings can vary considerably in their suitability for BIM modelling. Vector PDFs generated from CAD or other digital drawing systems may contain lines and other graphical information that can be interpreted more readily than scanned documents. Scanned PDFs may instead consist primarily of raster images and may require additional interpretation or tracing.

Common problems include low-resolution or distorted scans, missing drawings, inconsistent dimensions, conflicting information between drawing revisions, outdated documentation and incomplete information about building services or construction. Drawings may also describe the intended design rather than the building as actually constructed.

Where different drawings provide conflicting information, the discrepancy should be investigated rather than resolved solely by selecting one drawing without qualification. Information that has been inferred rather than directly established should be distinguished from verified information within the model where appropriate.

For existing buildings, the distinction between design information and information describing the actual condition of the building is important. An as-built or as-constructed information model can contain graphical and non-graphical information defining the delivered project, but the nature and reliability of the information depend on the records and verification available.

[edit] PDF to BIM and PDF to CAD

PDF to BIM and PDF to CAD conversion are related but different processes. PDF to CAD generally involves recreating or extracting graphical information from a PDF so that it can be edited as a two-dimensional CAD drawing. The resulting information is principally graphical.

PDF to BIM involves creating model elements within a BIM environment and can associate information and relationships with those elements. A BIM model may therefore support uses beyond the production of drawings, including coordination, analysis, information exchange and asset management. The appropriate approach depends on the intended use of the information and the information requirements of the project.

Neither process necessarily establishes the physical condition of an existing building. Where existing conditions need to be established to a high degree of confidence, measured survey or reality-capture techniques may be required in addition to existing drawings.

[edit] Information requirements and model scope

The required scope of a PDF to BIM conversion should be established before modelling begins. Factors may include the intended uses of the model, the elements to be modelled, the information to be associated with those elements, the required level of development, file formats, coordinate systems and project information standards.

BIM is not simply the creation of a three-dimensional model. It is concerned with the creation and management of information about a built asset throughout its lifecycle. Consequently, a model created from PDF drawings should be developed in response to defined information requirements rather than simply reproducing every visible line in the source drawings.

[edit] Related articles on Designing Buildings

• Building Information Modelling BIM
• BIM dimensions, maturity and levels of development
• As-built or as-constructed building information model
• Design information
• Construction drawing
• As-built drawings and record drawings
• Common data environment
• BIM execution plan BEP
• Step-by-step guide to using BIM on projects
• How to read technical drawings