ISO DIS 13567 - The Proposed International Standard for Structuring Layers in Computer Aided Building Design

SUBMITTED: December 1996
REVISED: April 1997
PUBLISHED: April 1997

Björk, Bo-Christer, professor
Royal Institute of Technology, Stockholm, Sweden
email:bjork@ce.kth.se http://www.ce.kth.se/fba/bit/people/bjork.htm

Löwnertz, Kurt
FFNS Gruppen, Stockholm, Sweden
email:kurt.lownertz@ffns.se http://www.ce.kth.se/fba/bit/people/kurt.htm

Kiviniemi, Arto
Studio Kivi, Helsinki, Finland
email:arto.kiviniemi@vtt.fi http://www.vtt.fi/cic/kiviniemi/

SUMMARY: Layering is a widely used method for structuring data in CAD-models. During the last few years national standardisation organisations, professional associations, user groups for particular CAD-systems, individual companies etc. have issued numerous standards and guidelines for the naming and structuring of layers in building design. In order to increase the integration of CAD data in the industry as a whole ISO recently decided to define an international standard for layer usage. The resulting standard proposal, ISO 13567, is a rather complex framework standard which strives to be more of a union than the least common denominator of the capabilities of existing guidelines.

A number of principles have been followed in the design of the proposal. The first one is the separation of the conceptual organisation of information (semantics) from the way this information is coded (syntax). The second one is orthogonality - the fact that many ways of classifying information are independent of each other and can be applied in combinations. The third overriding principle is the reuse of existing national or international standards whenever appropriate. The fourth principle allows users to apply well-defined subsets of the overall superset of possible layernames.

This article describes the semantic organisation of the standard proposal as well as its default syntax. Important information categories deal with the party responsible for the information, the type of building element shown, whether a layer contains the direct graphical description of a building part or additional information needed in an output drawing etc. Non-mandatory information categories facilitate the structuring of information in rebuilding projects, use of layers for spatial grouping in large multi-storey projects, and storing multiple representations intended for different drawing scales in the same model.

Pilot testing of ISO 13567 is currently being carried out in a number of countries which have been involved in the definition of the standard. In the article two implementations, which have been carried out independently in Sweden and Finland, are described.

The article concludes with a discussion of the benefits and possible drawbacks of the standard. Incremental development within the industry, (where ”best practice” can become ”common practice” via a standard such as ISO 13567), is contrasted with the more idealistic scenario of building product models. The relationship between CAD-layering, document management product modelling and building element classification is also discussed.

KEYWORDS: CAD-system, layering, standardisation

1. BACKGROUND

The use of CAD-techniques in building design has increased rapidly during last 10 years and is today common practice for producing building documentation. As a consequence of this, the need to transfer CAD-information between the different participants in a construction project in digital form, and not only as plotted paper drawings, has become of vital importance. In contrast to the layout and symbols of paper drawings, which in most countries is more or less standardised, the techniques for managing digital CAD-data are still in their infancy. A representative of a major Swedish design company recently jokingly remarked, that in major projects the specifications for information co-ordination now seem to be more voluminous that the design specifications themselves. This remark is a clear symptom of the problems caused by the lack of standard data structures for information management in integrated CAD design.

 The transfer between CAD-systems of the graphics contained in output drawings alone, which to some extent can be handled using standards such as the DXF-format, is not enough. Increasingly CAD-systems are used not as digital drawing-boards, but for managing integrated 2-D (or at best 3D) models of a complete building. (Excellent guidelines for end users and application developers have for instance been produced in Denmark (Abb 1993)). A system such as AutoCAD makes a clear distinction between model-space (containing the model of the building in world coordinates) and paper-space (containing output from such models in drawing sheet coordinates). As a consequence a prerequisite for efficient data transfer and sharing is that the information in such models must be structured and partitioned in standardised ways. In current CAD-practice quite elaborate layering schemes, often used in combination with the reference-file technique, provide the dominating method used to achieve this end.

In layering systems each drawing primitive is assigned to some layer. The user can then interactively decide which layers to show actively on the screen or to output on a plotter