Documenting the conventions
As discussed, CAD projects often involve bringing together datasets captured both in the field and at the desk-top. Several different people may be involved in the project in different roles at different times (e.g. surveyors, digitisation operators, CAD operators etc.). The data that they capture may be brought together as separate layers within a CAD model or as cross-referenced files. For instance, a CAD model may include both field survey data and data that have been digitised from maps, plans and photographs.
It is recommended practice for project managers to agree standard layer-naming (see CAD conventions) and file-naming conventions at the start of the project. These conventions facilitate the process of both data capture and in building CAD models.
Project layer-naming convention
Documentation should be provided for the layer-naming convention that has been adopted for the project. This should include:
|Name of Convention||The name of the layer-naming convention; this may be an agreed standard convention used by an organisation (e.g. the English Heritage layer-naming convention, English Heritage 2005) or a local convention agreed for a specific project. Full details of the layer name, content and drawing conventions should be documented unless details have been published, in which case it may be sufficient to provide a publication reference.
Repeat this information for each layer used.
|Layer Name||The name or code associated with the layer (e.g. OA-ROOF is the layer name associated with all roof timbers in the English Heritage convention).|
|Layer Content||A brief description of the content of the layer (e.g. roof timbers).|
|Drawing Conventions||Drawing conventions or any special icons and characters used in this layer. These can include specific font type, line type, drawing element and colour|
Project file-naming convention
Many organisations and individuals use file-naming conventions to identify details such as the project to which the file relates, its content, the version number and format. When depositing data in an archive it is helpful to provide documentation for these conventions. The information recorded should include:
|File Names||It is important to include some means of identifying the relevant activity in the file name, e.g. a unique reference number, project number or project name and to provide a brief explanation of any abbreviations used. For example, ‘GPS survey files start with a ‘g’ and are then indexed with a subsequent number: g1, g2…’ etc. Include version number information in the file name where necessary.|
|File Extensions||It is recommended that you reserve the 3-letter file extension and that standard file extensions are used to reflect the format of the data contained in the file, e.g., .dwg, .txt.|
|File Formats||Provide an explanation of which internal format is associated with a particular file extension, e.g. which version of .dwg or .dxf file format has been used.|