Unity for Architectural Visualization: For architects the walk-around 3D computer visualization is a fantastic marketing tool. This tutorial shows you how to use Unity to achieve modeling skills through step-by-step examples. You'll find the acquired expertise invaluable.

If you are in a situation where there is no suitable supported format, you have to rely on 3D conversion software. Even if your CAD system is supported, it makes sense to pass it through other software to fine-tune the conversion. You can export an AutoCAD model as a DWG file into 3ds Max and do the Unity conversion from there.

There are several typical problems that can occur when loading CAD models inside Unity. In most cases, paying attention during modeling can optimize the results considerably.

Missing back-faces

The following screenshot displays a rather typical SketchUp model of the Barcelona Pavillion, by the architect Mies van der Rohe. It was downloaded from the 3D Warehouse and modeled by user Cintilante 3D available at http://sketchup.google.com/3dwarehouse/details?mid=fabea878c454e119e8d39fcb58c495ea. When you open the model inside SketchUp, everything looks normal, but when loading it inside Unity, a large part of it seems to be missing at first sight.

Upon closer inspection, the geometry is actually available in the model, but can only be seen from the other side, for example, from the bottom. CAD software often displays front and back-faces of geometry, whereas Unity hides back-faces for performance reasons (namely, back-face culling). The order in which vertices of faces are connected defines the face orientation. If you don't pay attention to face orientation during modeling, gaps will appear inside Unity. This problem is not unique to Unity. Abvent Artlantis, a rendering companion software often used by architects, also hides back-faces. We have encountered this numerous times when students are trying to import SketchUp models. This is less problematic when you model with volumes or primitive objects, as they are usually well oriented to start with.

The solution is to either display both sides of the geometry, which effectively doubles the geometry to show on screen, or to flip the wrongly oriented faces in the modeling system, which is obviously recommended. In a correct model, only front faces should be visible. In the case of SketchUp, front and back-faces are both visible, but they have different materials applied, which complicates conversion to Unity.

When you model with single faces, this really becomes problematic. The face will only be visible from the front side and is missing completely when looking from the back. If you are modeling fences or other thin elements, such as glass panes, you need to either model them as thin boxes or export the model with faces for both sides separately. If supported, turn off back-face display in the CAD system, to better assess how the model will appear inside Unity. When using SketchUp, switch to the Monochrome Face Style, which will show all face orientation mistakes (back-faces) in a light blue color, as shown in the following screenshot:

Right click on the problematic faces and choose the Reverse Faces… option. Before you export any SketchUp model to Unity, switch to this face style and flip all blue faces. Beware that you might need to re-assign materials, as the front face material will be moved to the other side as well, which is not visible in the Monochrome face style.

Missing texture coordinates

Texture coordinates are the link between a texture image (for example, a picture of a brick wall) and the geometry onto which it is applied. Texture coordinates are stored inside the vertices of geometry, alongside geometric coordinates.

While most game modelers colorize geometry using textures, many architectural models contain plain and solid colors. When exporting to Unity, this becomes a problem, as faces will not have their texture coordinates properly set up. When you assign a material inside Unity or change the Base (RGB) texture, it will not be positioned correctly. Chances are that you'll only see a single color, usually the border pixel(s) of the texture or that the position and scale of the texture map on the geometry is inconsistent. The following image displays a basic brick texture and how it is mapped on the imported geometry. The stretched pixels indicate an incorrect mapping setup.

To alter these coordinates from within Unity, Unity requires separate tools and is really cumbersome, certainly when the original model changes. Always assign textures in the original model, even if the texture itself is only a placeholder.

Let's explain this with an example that could be applied in most BIM authoring software applications.

When the architect creates the design, he or she can set up the model in BIM software as an assembly of building entities positioned on stories. At any time, the model can be shown in a 3D view. However, many possible 3D views can be created. Imagine that it has been decided to visualize a first design proposal to the client. The model can be set up at a moderately detailed scale level (for example, 1:100), with the main fixed furniture visible, albeit without some of the model details, such as door knobs and closet handles.

In addition, all technical installations, which have been created as part of the model and which are important mostly for the engineers and contractors, have been hidden in the model. It was decided to mainly show the atmosphere of the design through materials and lights and the layout of the facility.

The particular 3D view is then exported into a Unity compatible format and placed inside a separate folder underneath the project Assets folder. We skip the many possible interoperability issues in this example and focus on the overall workflow. Within Unity, the model is imported and positioned in a scene, to be explored in the "game" by the building owner, who receives the Unity project as a standalone application.

Although the architect imagined the building owner not to be interested in the technical details, there are some worries about the feasibility of placing the large ventilation shafts and ducts in a non-obtrusive way, so the architect is asked to update the design. In the BIM authoring system, a new 3D view is created, which only displays the technical installations as 3D geometry and this is exported as a second model for Unity. This model is added to the scene and a small GUI is scripted with two simple buttons to toggle the visibility of the architectural and the installation model upon request. In Chapter 7, Full Control with Scripting, we explain how to provide such an option to the user.

After the next client meeting, some design changes are requested. The architect adjusts the model in the BIM authoring software and exports the models again from the two views that have been set up, overwriting the first export files. The model inside Unity is updated automatically and the new version of the interactive application simply has to be built again with identical settings. While the design model changes took some effort, the time it took to update the real-time model inside Unity was negligible.

The scenario pictured here requires some experience to set up a properly, but it is not far-fetched at all and presents an important added value of using BIM authoring software for a real-time architectural visualization. The master model contains the actual, current version of the design, which can be updated at any time, and is completely in sync with the technical drawings, the presentation drawings, or renderings. The real-time model can be updated with minimal effort to integrate changes into Unity. This makes the process accessible in an architectural office, although dedicated visualization teams can create more extensive and graphically refined models, when specializing in the Unity part of the workflow.

It is strongly advised to not try to make a single model encompassing every part of the design. It is much more efficient to set up separate complementary models, such as architectural, structural, and technical subsets. They can be assembled inside Unity and toggled from a simple user interface.

While the scenario depicted above seems easy and straightforward, the interoperability poses particular problems. Most BIM software lacks the direct support of the FBX format and even when available, this export is often not optimized for Unity.

Many of the pitfalls we discussed about CAD software are still applicable: architectural BIM models often use plain colors for materials and often lack texture-mapping information.

The problem of back-face culling is less prevalent, as the BIM software tools generate suitable polyhedral meshes where the face orientation is set up properly apart from maybe the glass panes, which are often modeled as a single face only.

There is a huge risk of adding too much geometry into the model, especially when furniture is included or (even worse) if trees and cars are included. While BIM tools often support a good library of common building objects, such as chairs, tables, but also windows and doors, they are typically not set up to minimize geometry. For example, a closet model also contains geometry for the inner parts, even though they are probably never seen in the real-time model, unless the model is set up to allow doors to be opened.

If supported by the BIM software, it is advised to set up the objects to be scale sensitive, allowing them to hide large parts of the geometry when displayed at a larger scale. This can then be used as a setting inside the particular views that have been set up for export to the real-time model. Some applications, such as ArchiCAD also provide a resolution setting for most curved objects, which controls the tessellation into polyhedral meshes.

To make matters worse, the export process often creates each object as a completely new geometric object, disregarding instancing in most cases. If you place 20 chairs in a restaurant space (which is easy to do in a BIM system), each chair will count as separate geometry in the exported model.

If feasible (it often isn't), create separate singular models for such objects and use Prefabs inside Unity, which places a much smaller burden on a scene, as repeated geometry will be optimized by the game engine. We will learn more on optimization in Chapter 5, Models and Environment.

When trying to add a rotation or sliding animation for doors and windows, it is often impossible to separate the moving parts from the static ones. It may even be necessary to hide them in the model and replace them with custom Unity animated objects, which takes much more effort. As a simple compromise, you can disable collisions on these objects or set them up in their open state in the BIM software, so they don't hinder navigation.

3D modeling systems and recently BIM authoring software can be extended with plug-ins or add-ons. A good example is the BIMx module, developed by Graphisoft, which is integrated into ArchiCAD. It allows a direct export from the ArchiCAD model into a standalone application, including the player and the model. It can be played on a computer (Mac or PC) or loaded into the free BIMx app for Android or iOS devices, allowing real-time navigation through the project, with only minimal effort. The following screenshot displays how an ArchiCAD model looks inside the BIMx software.

Other interesting systems that are worth mentioning are Autodesk Showcase, Act-3D Lumion, LightUp for SketchUp and Viso3D, also for SketchUp. There is also REALIS3D, which is a dedicated architectural visualization system, built with Unity.

When requiring real-time navigation for a project, it is good to consider such solutions. What they provide in ease-of-use (for example, single click export, built-in features), they often lack customization options. User interaction and the method of navigation are commonly predefined, without the possibility to add other forms of interactivity or visualization.

It is precisely this customization and flexibility that can be the motivation to master a real-time authoring system, such as Unity, at the cost of added effort and complexity. You could re-create most of the functionality of BIMx inside Unity and once this level of interactivity is prepared, using custom scripts, there is nothing preventing you to go a step further. Since this book is about Unity, we will not go into further detail about such dedicated systems.

While we would prefer to claim that any modeling software is equally usable, two combinations are worth mentioning specifically and they are based on using software from the same vendor in both cases.

When using CAD or BIM software from Autodesk, it helps to pass through DCC software that is also provided by Autodesk. AutoCAD or Revit models are best passed through 3ds Max or Maya before converting to FBX into Unity. This is especially important to reflect model changes. AutoCAD models are usually passed as DWG files to Max or Maya. Set up correct material properties and texture mapping and either save the file directly inside the Assets folder (to have Unity call up the translation in the background) or export to FBX into the Assets folder. The former is slightly more convenient, but the latter gives you full control and is usually the preferred choice for experienced users.

This is equally true when using software from Nemetschek (or one of its daughter companies). ArchiCAD and VectorWorks models are best passed through CINEMA 4D, before converting to Unity, for exactly the same reason. The Exchange plug-ins for ArchiCAD and VectorWorks optimizes the model exchange with CINEMA 4D and automates model updates. You can set up materials and textures and still refine the model in the original creation software. CINEMA 4D models can be placed directly inside the Assets folder.

As always with interoperability through add-ons, success depends on particular software versions and supported platforms and the fact that a software update of one application can break compatibility with the other one. Alas, this is beyond our control.

You can also be confronted with permission problems. When you use the automatic conversion process, Unity copies an FBX exporter module in the supported application's add-on folder, which requires administrative permissions. On Windows, you have to launch Unity as an administrator at least once to have this process completed.

With both the Autodesk and Nemetschek applications workflow, you can reload the architectural model, while preserving applied materials, mapping, or animations, and consequently reload the FBX model inside Unity while preserving the additional settings over there. The following screenshot gives an example of an ArchiCAD model that is exported to CINEMA 4D and loaded inside Unity:

Based on reactions in user forums on Unity (for example, the Unity Community at http://forum.unity3d.com/forum.php) or one of the related DCC software programs, many people actually suggest ignoring the automatic conversion and leaving the native models (for example, MAX or C4D files) outside of the Assets folder. They would rather perform the conversion manually. This allows more control, for example by splitting the model up in smaller chunks, so they are easier to manipulate inside Unity. This is also required when you collaborate with others and not everyone has the Unity or modeling software available on their machine. In that case, the artist responsible for the 3D model can work on a provided FBX, while the designer responsible for the building model can continue working, and export the model when updates need to be integrated.

The following figure summarizes several workflows that are known to work well for architectural visualization. Bold arrows are the recommended pathways for optimal integration.