Are CAD Layer Naming Standards in Disarray?
MYCADLAYERS was originally produced before ISO/DIS 13567 (International CAD Layer Naming Standard) and the AIA Layer Naming Standard and was considered by the ISO Standards Association during the submissions/comment phase of the Standard.
Although MYCADLAYERS was and still is simpler and more compact than any National Standard and most private or customized standards its principles comply with the intentions of all National and Professional Standards.
Do Layer name Standards really work?
A search of the web for “CAD Layer Naming Standard” appears to reveal that in spite of several attempts to produce a universal CAD Layer Naming Standard little real standardization has actually occurred. There are various National and International Standards and possibly hundreds if not thousands of Office standards still in use throughout the Globe.
One must ask why these efforts, that go back to the ‘nineties, have not resulted in effective standardization across offices let alone countries or continents. I could be wrong but my guess is that they are too complicated, too difficult to administer, not very useful from a drafting point of view, and not last and by no means least, much too difficult to execute at the CAD User Interface. This is not surprising as the complexity of published standards discourages use. By way of example have a look at AIA Layer Naming Standard . Taking the AIA Standard (merely as an example) it acknowledges the existence of an ISO/DIS 3567 and admits to not really complying with it and insists on maintaining its own validity. The existence of so many Standards is surely the the most convincing indicator that something is not working.
Most Standards try to take apart the structure of drawing data and assign everything from legal responsibility to how tall an object is. Well that’s a bit of an exaggeration but the point is that little emphasis is given in any of the standards as to how such layer names are to be used for other than the drawing and printing process. There always seems to be a desire to lead to BIM i.e. extraction of building quantities but no explanation as to how this might be done or even if such a process is possible from the Standards as currently formatted. For most CAD users the main objective is usually black lines on white paper with no need for or indication of all the detail included in layer names.
Unless Building Information Modeling (BIM) is the objective of Layer Name Standards there is little practical use for several of the fields particularly the so-called “minor” fields in the layer names. Yes there will be benefits to the CAD operator in being able to see that the model is complete and logical but it cannot be overlooked that unless it is a fully detailed a 3D model it cannot be used for material measurement or as a substitute electronic specification. The only practical use for supplementary information about drawing objects in a layer name is to allow management of the data during drawing production and plotting, particularly differentiation in plotted appearance by virtue of color (pen width) and line-type. As far as I know no published standard includes color or Line-type as Layer name fields in spite of the fact that color and line-type are fundamental to interpretation of drawings and are commonly used to distinguish different data categories.
The Agent field is also questionable. When one comes to study the use and effect of XREFs the inclusion of an Agent field might be considered to be redundant. The only value of an Agent field is if a true multi discipline communally owned and edited single web-based model is maintained. The reality (in building at least) is that most general models will be owned and maintained by the principal designer; usually the Architect who will manage the addition of other disciplines by XREFs that will automatically identify their specific author (Agent). In practice it is most likely that the Architect and each consultant will "own" their own drawings and OVERLAY XREFs from the other consultants. The only deviation from this that I can think of is if a facilities management office required all data to be in a single model but but with a uniform layer naming system that still required author identification. The probability is however that the consultant's layer naming is unlikely fit the required Standard.
Surely any authority producing a Layer naming Standard ought to provide or at least encourage and facilitate an automatic layer naming program. It’s not that hard. Once you have a standardized layer naming method it is easy enough to write a program to semi-automatically create layer names at the keyboard or through dialogues. Years ago; prior to the release of ISO/DIS 3567 and the AIA Standard MYCADKEYS was using a layer naming standard that enabled the rapid and accurate creation and management of layers for both editing and plotting.
National Standards vs. MYCADLAYERS
A big difference between MYCADLAYERS and most Standards is that MYCADLAYERSnot only allows automatic layer management of multi-function drawings but also multi-level or multi-section models to view edit and plot different drawings from the same single model. MYCADLAYERS provides both a dynamic dialogue and a Command line interface to layer control but for keyboard users layer management is more quickly achieved through aliases that mimic the dialogue box. Both methods automatically supply correct structure and length layer names with correct color and line-type.
ISO/DIS 13567 rules:
- Intended to provide a universally applicable conceptual structure.
- Layer names are constructed of several fields, some of which are mandatory and others optional.
- Fields are designed to be exclusive, that is, only one type of data per field.
- The structure is to allow migration of data from pre-existing layer name systems.
- Overly complex structures are to be avoided. Syntax and data coding should be designed for easy interpretation and manipulation.
- The Standard defines:
- the concepts to be coded in each of the fields,
- the order of the fields,
- the field lengths and sometimes coding..
- The Standard allows for variation on a project by project basis provided the procedures used are documented in a way that allows future retrieval of the layer information.
- It is emphasized that the ISO default is a starting point for defining national or project standards and is provided as a neutral standard for archiving or data exchange.
- Provided that the Mandatory fields required by the Standard are always used, conceptual conformance permits Optional fields to be used in any order and length, though the conceptual content of each field can not vary from the definitions in ISO/DIS 13567.
- If a project layer system varies from the ISO default, documentation must be provided for the project specific system identifying and describing all valid values of all non-default fields.
What about MYCADLAYERS?
First of all MYCADLAYERS complies with both the US and European Standards but within those rules is much simpler to apply and makes more sense from a drafter's point of view. Provision is made for both long and short names depending upon the project. What is most important is that the process of creating layers, managing their properties, viewing and printing are all semi automated to the point that it is difficult to make an error. There is no need for a schedule of layer names and no need to scroll through extensive lists of layer names.
MYCADLAYERS uses either five or twelve characters to construct either three or seven data fields respectively:
Group 1 Object, Pen number, Line type (5 characters)
Group 2 Drawing Status or Phase/Stage (1 character)
Group 2 Drawing type, View point, View ID. (6 characters)
Group 1 is mandatory and provides the core description of all objects and is the minimum layer length for simple projects.
Group 2 is added only when required to define Status or Phase/Stage.
Group 3 is added to allow separation of drawings by type (e.g. electrical) and level (e.g. level-02) but only used if OVERLAY drawing is used.
Some standards include an Agent field to identify the author but this is unnecessary in MYCADLAYERS as this is either implied in the Drawing Type field or is clear from Xrefed data.
Theoretically there are no limits to drawing model size but a true multi-profession multi-function single model seems an unlikely common achievement for the foreseeable future. Particularly since at present multi-user software is the exception rather than the rule and even the most efficient machine would be laboring on a multi discipline model of anything larger than a small block of flats. Organizing a group of consultants to work on an on-line single shared model is also an ambitious objective.
Agent: Not used.
Object: 3chr (Equivalent to the ISO Element field)
Object provides a three character field to describe data type. There are two possible data sources: data owned by the author of the current drawing and data imported from another discipline. The owner's data has two forms: buildables such as walls and reference data such as text, dimensions reference symbols etc. Buildable elements might be a material or trade e.g. WAL (wall) while imported data would be information from another discipline such as Structural Engineer e.g. ENG (engineer). Imported data such as mechanical or lift services designed and specified by others does not usually require a detailed description since it is not the responsibility of the author of the current drawing and probably should not be editable. Imported data is usually simplified and indicated by outlines only and a single description is adequate.
Reference objects (text, dimensions, labels etc.) may optionally have their layers associated with the objects to which they are related or have one generic description such as REF.
It is believed that the MYCADLAYERS approach to object codes is more comprehensible to the CAD operator than the ISO three digit CISfb numbering system. It is more closely related to the way in which CAD layering is really used and subsumes the ISO Presentation field that would otherwise be necessary. In most cases the characters are the first three characters of the key word. In the case of duplication, which rarely occurs, well known abbreviations, acronyms or mnemonic substitutions may be made for the lesser used Object e.g. PLAster/PLastiC. Although in some professions an index of codes might be necessary little difficulty has been experienced in building drawings in the thirty years of MYCADLAYERS use. It has been argued that four characters provides more flexibility, however extensive early trialing demonstrated that four characters created more problems than it solved.
Pen: 1 chr (Not used in ISO - Refer to ISO Presentation field)
Autocad colors are used to reference a virtual plotter ;Pens by color number. MYCADLAYERS provides a choice of up to about 45 pens using numbers 1 to 9, letters A to Z and !$%^&+-@~ etc (when using extended layer names). Refer to later discussion of Colors.
Line-type: 1 chr (Not used in ISO - Refer to ISO ;Presentation field)
Autocad standard Line-types are numbered by MYCADLAYERS in the order listed in the Autocad manual (alphabetical) eg 1 = Border, 2 = Center and so on. You might, however, use a few alpha characters also; thus allowing (not sure why you would want to) forty or so line types to be distinguished.
For some special objects to which line-type is irrelevant (i.e. their line-type is always Continuous) the line type field may be used to indicate reference information eg T = Text, H = Hatch, D = Dimension. The ISO exclusivity rule is not breached as these two concepts do not occur concurrently.
Status: 1 chr (similar to Phase as in ISO) Not needed in five character Layer names.
Typical codes for project stages might be:
- D Demolition
- E Existing
- N New
- O Obsolete
- P Proposed
- R Reuse
- S Store
- - global
Drawing type: 3 digit number
(Similar to ISO Work Package)
Drawing type identifies the purpose for which a drawing is produced e.g. general arrangement, electrical layout etc. MYCADLAYERS allows for up to nine different drawing types in any one project. Refer to later discussion of Bit-codes.
Viewpoint: 1 chr
Viewpoint indicates Plan, Elevation etc
View ID: 2 chr
View-ID Indicates floor level, elevation number etc.
Other fields appearing in the ISO Standard:
ISO provides three additional fields:
Presentation is subsumed in the MYCADLAYERS fields recommended above.
Sector is partly covered by Viewpoint and View ID and when you get to the sector sub-fields of Zone and Building these are most likely to be covered by using separate drawings.
Most often Scale is implicit in Drawing type. For example if details are to be incorporated in the same model as general arrangement information this can be provided for in the Drawing Type code number e.g. a Fit-out drawing. Experience shows, however, that details (particularly large scale details) are drawn quite separately and related to general arrangement drawings by way of call-outs and coordinating lines.