The complexity of the architectural visualisation process can soon - if you're not careful and organised - become quite overwhelming. There are many elements that need to be 'juggled' to achieve the best results, such as composition, geometry detail, lighting detail and texture detail.
A current project for a luxury interior apartment in London calls for some very detailed work with regard to fabrics. The interior designers have selected a beautiful array of fabrics, metals, timbers and wallpapers, each requiring very careful attention.
More often than not, a material swatch is only a few square centimetres in size, yet needs to be applied to entire walls (for wallpaper) or soft furnishings (chairs, sofas, cushions etc) in our 3D model. If we were to simply scan or photograph this small swatch of material and duplicate it to fill whatever geometry it is being applied to, you would see a distracting repeating pattern that shouldn't be there. This is largely because any given swatch will have imperfections from one edge to the other. This could be a lighting falloff across the swatch. It could be an slight crease in the sample. It could be a few bits of dust, fingermarks or scratches. All these things, when duplicated, will yield pretty nasty results!
To do the job properly, each sample of material must instead be broken down into discrete elements. These elements are things such as the reflectance, the diffuse pattern, the grain, the bumpiness, the changing tones... Each material has very different characteristics, and it is our job as 3D artists to study these characteristics and replicate them as closely as possible.
The diagram above is a breakdown of just one texture for a swatch of fabric on a plush armchair. You can see from the number of connections how complex a material can get (and this one isn't the most complicated!). There are three or four layers of texture just to do the job of creating the underlying diffuse tones. On top of that, we have a couple of layers of bump to replicate the roughness of the surface. Elements of the diffuse and the bump are combined in a slightly different way to simulate the subtle reflections that vary depending on the angle of view. Below, you will see a snapshot of the material that the above diagram creates.
Scale this type of complexity up to cover all the materials in one scene, and you can appreciate just how involved CGIs can become.