3D Modeling Lab: Introduction to the Building and Display of Real Time Interactive Models

Basic Elements

There are basic steps and critical issues integral to the building and display of interactive models:

• Planning: Optimizing, Reducing, Focusing, Timelines.
• Project Files: File Structures, File Locations(Pathnames), Moving Project File Systems.
• Building Models: Application, Textures, Colors, Lighting, Speed.
• Importing Models: File Types, Limitations, Changes To Hierarchies, Texture Mapping.
• Combining Models: External References, Limitations.
• Shading Models: Shading, Lighting and Texture Map Resolution and File Types.
• Testing Models: On Modeling Workstations, At The Venue.
• Navigation: Navigation Tools and Options.
• Display Formats: Spherical, Flat Plane, Stereo, Non-Stereo.
• Display Environments: Portal and similar facilities, mobile facilities, mobile platforms.
• Rehearsing: Practice Navigating, Scripting, Troubleshooting.

Planning

The greater the number of models, polygons, textures, processes and files a project uses the greater the opportunity for errors to occur, and the slower the overall speed of navigation and development. Projects that do not start with organization can quickly become unmanageable and will not be finished on time. Thus it is very important that before the modeling starts, projects be carefully planned with an emphasis on refining what it is that needs to be shown, on staying focused on that, on reducing the number of elements to a minimum and on establishing a realistic production timeline. It is also important to understand the various stages of production and display, what their technical requirements might be and how much time they will take.

Project Files Setup

How a project is stored within a file system is critical to how quickly and easily it can be accessed, developed, moved, updated and displayed. There are a number of options from flat to hierarchal, that can be used, depending on your preferences and upon what the project hopes to accomplish. It is important to keep in mind that when the model is “finished” you will go on to display the project in a real time, virtual reality environment separate from the environment you created the model in. That will require that all of the constituent files be moved to some distant file system. Regular updates to the files on that remote system may also be necessary and must be accomplished quickly and easily.

How the location of files(models, textures, referenced) is defined, is also critical, especially when the files are moved between file systems. Absolute pathnames are problematic. Also important is the fact that all of those working on the project have access of one kind or another to most if not all of the project files. If it is a team effort it is often best to have a file system that all members have access to. It is critical that you have a clear and consistent strategy when determining project file structures, files access, how files are updated, how file locations are defined, and how files are distributed, both in the development and in the display environments.

Building Models

It is important to understand that the applications that build the models are not the same ones that display them it in an interactive, real time, virtual reality environment. At this time the preferred application for constructing interactive, real time models is Multigen’s Creator. The applications for display are OpenGL based and include Performer, Juggler and vrNav. Creator produces Openflight or FLT files which Performer/Juggler/vrNav can load, along with all of it’s specialized instructions and file references.

Although models can be built using other applications and exported as FLT there have been repeated problems in getting those models to perform properly in an OpenGL environment. The various economies, instructions and orchestrations available in Creator are also not found in other applications. Until that changes we recommend that models be built using Creator, or if they are built in another software, that they then be imported into Creator for finishing.

Creator has tools for building, importing, integrating, organizing, processing and shading 3D models. It is very good at minimizing the number of polygons that constitute a model and has a variety of orchestration tools specific to real time, interactive display. In creating an interactive model it is important to keep in mind that the number of polygons and textures maps it utilizes will directly influence how well it performs. The more polygons the slower the model. The greater the dimensions and the number of textures the slower the model.

Creator also has tools for assigning, editing and mapping textures onto models, and rudimentary tools for setting up and calculating lighting. While the texture tools are more than adequate, the lighting tools are quite basic and do not allow for most of the standard specular qualities, shadows, and radiosity effects. For more realistic or convincing shading effects it is better to utilize another rendering application such as Lightscape.

The basic workflow for Creator is to create your polygonal models, set up all of the necessary effects, assign, edit and map textures, and then export as FLT file type to be displayed using vrNav. If you have models that were made previously, or if you wish to do your basic modeling in another software, ATS does support applications and plug-ins for translating a variety of file types into FLT. These projects should still be imported into Creator, tested for errors and fine tuned. Be sure to check with ATS personnel to ensure that the file types you might wish to convert are supported.

Importing Models

It may be that you have already invested a lot of time in building models in some file type other than FLT, or that you prefer modeling in some other application, or that models need to be brought in from other applications and integrated with models in Creator. While Creator is rather limited in what it can open or import, the Modeling Lab does support a number of applications that can translate to or directly output FLT files. Okino NuGraf for instance allows for a wide variety of conversions to or from the FLT file type.

Again keep in mind that in converting models there is always the risk of some compromise, some loss and some time spent in making repairs. Pathnames may be changed, texture files may become “lost”, texture maps may be misaligned or not aligned at all, shaders from some applications may not render the same or at all when converted to the FLT filetype. These compromises vary in nature and in degree depending on the modeling application, on the converting application, and on the versions used. Always be sure to check the integrity of models after they are converted.

Also keep in mind that Creator, and the FLT file type, support a very limited range of the shader qualities found in other modeling applications and none of the effects. For instance, while transparency is supported, bump mapping, noise, procedural textures and glows are not. While DOF and Transformation matrices are supported, particle effects, fur, motion blurring and lighting effects are not.

Combining Models

Creator has tools for combining dispersed FLT files and integrating them into one, efficient polygonal model. The primary tool for doing this is called External Referencing, which uses files names, directory paths and an external reference node to read in and manipulate other FLT files, without having to build them or convert them locally. External references can be read in any number of times and transformed any number of ways. They serve to streamline the organization of larger, team projects, and the modeling and editing of large databases, because models can be split into constituent parts, all of which can be edited separately, and then easily reunited. It is important however to maintain tight control over the location of referenced files, and to note every time they are moved or renamed, otherwise the pathname of that reference will no longer be valid. Again, it is important that these files be carefully organized and saved to specific locations.

Shading Models

Creator also has tools for assigning, editing and mapping textures onto models, and rudimentary tools for setting up and calculating lighting. Textures in Creator are based on specific image file types, and also support alpha(masking) channels or files, such as RGB alpha channels and 8 or 16 bit Intensity-alpha files. Textures can be mapped, scaled, rotated and masked, as well as processed through a texture editor. The format of the file is also very important in the sense that it’s dimensions must be a factor of 2(8,16,32,64,128,256,512, 1024,2048). Thus a resolution or format of 256x256 pixels would work as would 256x1024. Image files that do not meet these criteria may display correctly in Creator but they will distort or fail to render when displayed in Performer. The resolution of an image also effects the speed at which it can be flown by a computer. The larger the number and resolution of the images files used by a model or project, the slower the overall speed of navigation and development.

While the texture tools are more than adequate, the lighting tools are quite basic and do not allow for most of the standard specular qualities, shadows, and radiosity effects. Creator is capable of providing a base or ambient illumination for models, and in theory does have somewhat advanced light effects, but by the time the models are displayed in Performer, their textures appear rather flat and unnatural looking, the shadows are not at all convincing and the lighting bears no resemblance to reality whatsoever. This may be perfectly adequate for most scientific models, but it often falls short of what is needed for architectural models and environments.

To provide for more realistic or convincing shading effects it is better to export the models and their related textures files to another rendering application such as Lightscape, where the texture maps can be processed and then exported back into Creator for finishing. Although this technique does not yet allow for real time, interactive lighting effects it is far more convincing than the basic lighting effects provided for by Creator.

Testing Models

It is important to begin testing your models in OpenGL based display applications as soon as is possible. Since the modeling and the final display applications and hardware are different they will not render the same models in the same way.

All of the modeling workstations support Performer, Juggler and vrNav which act in concert to navigate and display models. This makes it possible to fly your models on any workstation using a command window and either perfly(Performer) or vrNav commands. Using these applicaitons, geometry, textures, various effects, pathnames, and external references can all be tested. The modeling process should become a regular back and forth, between building in Creator and viewing with perfly or vrNav.

Once initial testing is done on a workstation display it is important to move onto the final display venue(s) itself to get a firm grasp of the navigational space of the model. It is critical that you test projects in their final display environment, or one very much like it. The display environment of a single screen, or of a synchronized multi screen system is completely different than the three projector, large screen format of a Portal. If the projects final display space will be a single screen, using flat plane archives, then do your previewing using a like environment.

Navigation

ATS provides a range of navigation devices to “fly” devices in the Portal and is constantly experimenting with new ones. Research is always being done to improve upon these devices so the list is not static, but right now Tracker and Stinger are supported, and other devices, such as one based on the three button mouse are being adapted. Each one is a unique navigational tool with its own special features, and once your models are near to completion these devices should be tested in conjunction with the various display formats, and one selected. All of these devices take some getting used to, and it is highly recommended that you set aside the time to practice navigating.

Display Formats

Models can be projected in the Portal and in like facilities, according to a variety of display formats, including flat plane mono, flat plane stereo, spherical mono and spherical stereo. Each one of these formats provides for a distinctly different viewing experience, and each one has distinctive advantages and disadvantages. Although the modeling process is the same for all four, it is important that a decision be made as to which one the project will eventually be projected in, such that the models can be fine tuned, and the necessary hardware and files provided.

Rehearsal

Strictly speaking, rehearsing presentations is not part of the modeling process, but in order to present your projects in the best possible light and to take full advantage of all your effort, it is crucial that you rehearse the ways you will introduce and navigate your models. Always leave ample time at the end of the “production” process to practice navigating, to go over your monologue(s) and to troubleshoot your models in the final venue or presentation Portal.