The Traditional Approach
Construction drawings have traditionally been 2D, using linework and more recently 3D, using solid objects. There has been only a small amount of embedded intelligence available to be made use of. Object properties have been largely limited to geometric properties such as position, length and angle.
Any intelligence that was there had to be added manually and then extracted manually later.
Example: A manhole block could be inserted into a drawing with attributes such as type, diameter, material, invert level and cover grade but that information had to be added to each manhole as it was inserted. To create a schedule of manhole data involved manually extracting the data which was then in a spreadsheet format but no longer associated with the drawing.
Building Information Modelling (BIM):
BIM works on the principle that the model contains all of the project information in a single database format, which is then graphically displayed as a 2D or 3D view.
The model database is populated by adding elements to the model graphically. For example, if a new door is added to the model, it's existence and associated properties (height, width, material, etc.) are added to the database as well. The database will update to reflect any changes made to the elements and information can be extracted at any time. There is no longer a reliance on a completed drawing. Furthermore, extractions can be made using a phased approach, thereby introducing a 4d or time element to project control.
Autodesk Revit Architecture is one of the applications which exist that have been designed to enable BIM and is structured in a hierarchical format defined by categories, families, types, and instances.
· Categories: A category is a group of the elements that make up a model.
o Typical categories of Model elements include walls and doors
o Typical categories of Annotation elements include dimensions and section tags
· Families: Families are sub-groups within a category. A family will contain elements that have a similar graphical representation. All elements in a family will have an identical property set, although the associated values will vary between elements. Typical families include single doors and cavity walls.
· Types: Types are further sub-groups within each family.
o A typical door type could be specific size of a door. It could also be a specific style (for example, Georgian door)
o A typical wall type could be specific width of a wall. It could also be a specific style (for example, Brick/block with internal plaster)
· Instances: Instances are the physical elements that exist within the model, of which there may be many. Each time a type is added to the model, a new instance is added to the database and shown in the model. The properties associated with that instance are available to be interrogated.
BIMMeasure takes advantage of this ability to create drawings based on intelligent models by talking directly to the exported properties from the model database. Any property that is associated with an object can be extracted and used to create measurements.