This article is not for pros. It is for those who are totally dim about BIM, just like myself a few months back. Now I am not that dim, and felt it would be good to share it in the same way I began to understand real BIM. If you already know what BIM is, don’t read this.

OK, here we go, ...  Assume that I wanted you to build a building, a security hut, in my plot of land. As we normaly do, I could have given you a set of drawings (and technical specification). But, instead of those, I give you a document which reads as follows.

I have a building here. Its Finished Floor Level is 300mm from existing ground level, Ceiling Height is 2500mm. The External Wall is 225mm wide brick work wall in 1:5 cement : sand motar in English bond with 25mm rough cement plaster on both sides. The External Wall start 3000mm north to the west corner stone of the plot of land; runs 4000mm to the north, then 2500mm to east, then 4000mm to the south, and then to the start point. All measurements of the External Wall are to the finished external face. External Wall Bottom is at Finished Floor Level and External Wall Top is 300mm above the Ceiling Height. External Wall Foundation is 300mm wide and 600mm deep centre aligned to the External Wall. Main Door is located at the centre of southern External Wall. Main Door is a timber door with ...

... and so it continues until I tell everything about the proposed building. When I write everything, and if I write them accurately, don’t you think you can build it exactly as it describes. Sure you can, unless it explodes your brain out when you keep on reading trying to visualize it in your mind. By the way, what this document should be called? Is it a technical specification, a client’s brief, or a performance specification? The best I can call it is “BIM”.

A Building Information Model, or a BIM model as they call it (note the redundant M), is a detailed description of the building like the one above. Only difference is, it is written in a language (words and grammar), which a computer can read and understand. The term ‘Syntax’ is often used to describe this type of writing to emphasize on the importance of rules and principles of the structure of language. Not like the human brain, a computer can read, interpret and manipulate lot of information quickly and accurately. Once the building is defined using this Syntax, the computer can interpret it and ‘visualize’ it, which they call ‘virtual construction’.

A BIM model is far different from a drawing which only contains lines and curves that does not give much meaning for a computer to interpret. But, of course we, the human beings, can make something out of those lines and intepret them to be walls, windows, columns, etc. through combined skills from training and intution, showing our superiority to computers. But, when we use BIM to represent our building, the computer become capable of its meaningful interpretation, then it's computational power to manipulate the information to virtually construct the building in its memory. Thus, the sole reason we describe our building in BIM language is to take the advantage of computational power of modern computers.

When the building is virtually constructed within the computer ‘memory’, we can get a lot of information about the building as we may want to get from the physically constructed building, and probably much more due to practical difficulties related to physical constructions. For example, we can find if the building can withstand a certain degree of earthquake, we can see if the circulation space is adequate in an emergency, and we can see if a dark colour or light colour would be nicer for the facade; all through virtual construction before the actual physical construction. It is like you construct the billiard table in your imagination and simulate the movements of the balls in your mind using the logics of velocity, weight, rebound effect, etc. before you actually hit the ball. ... ‘got it? So, it is not just about 3D (three dimensional) visualization, it is a visualization of all relevant characteristics of interest.

Different types of software have been developed to visualize BIM models for different purposes. Each software will only use the relevant information from the BIM model and interpret them. However, most software generates 3D views for the user to see on the computer screen to help them to understand it better. Generation of 3D and 2D (two dimensional) views is done using the description of the building elements and spaces. The technique is simple as a draughtsman doing a drawing by reading my description of the building above; however we should understand that automating such a thing to be done by a computer is the advancement of the technology. Not all the BIM software necessarily generates 3D views.

Authoring (writing) of the BIM model manually using the BIM Language Syntax is not practical;  the writer will probably end up at mental hospital. Hence you will survive as there is no BIM model for you to read. Software vendors have been kind on the mankind and have developed software which we can use to model the building in graphical and other user-friendly interfaces. Then the software will automatically author the BIM model for us. For example, I may draw a wall on the computer screen using the graphical tools, and define its type by selecting from a menu; then the software will write the model as per the syntax for me as below.

#9792= IFCDIRECTION((-1.,0.,0.));
#9796= IFCCARTESIANPOINT((12.,0.,0.));
#9800= IFCAXIS2PLACEMENT3D(#9796,#36,#9792);
#9803= IFCLOCALPLACEMENT(#593,#9800);
#9806= IFCWALLSTANDARDCASE('16DNNqzfP2thtfaOflvsKA',#13, 'Wand-Ext-ERDG-4',$,$,#9803,#9876,'A6C3DE63-3731-4F6A-94-7E-DE8A8295779F');
#9825= IFCCARTESIANPOINT((0.,0.));
#9829= IFCCARTESIANPOINT((12.,0.));
#9833= IFCPOLYLINE((#9825,#9829));
#9837= IFCSHAPEREPRESENTATION(#51,'Axis','Curve2D',(#9833));

Note that the above is only a tiny part of a BIM model. A BIM model is infinitely long, you will never end reading it alive. However, BIM model’s syntax receive little or no interest in day-to-day BIM applications since this is for the software to read; and we, the users, only read and write in more user friendly, easy to understand, graphical and textual formats generated by this software from or for BIM models. Therefore, your effort to read and understand the above part of BIM model is unnecessary.

You may feel that you are still dim, but you are not. What you did not get are just jokes. Forget about them. Read “What is BIM”. If you still fail to understand it, drop me an email. If this article helped you someway, I’ll be grateful if you let me know that too.