3D Models and Assets

The ability to interact with and collaboratively work on 3D models in a virtual space expands the ways we understand them and enables shared experiences that may be a near substitute for working together on real physical objects in person. Sometimes interacting with 3D models even surpasses what can be done in the real world, as the digital nature of objects permits real time adaptation and modification of them without the investment of costly resources. This is the case, for example, in the automotive industry, where engineers can conduct design reviews and make changes on the spot, or in architecture, where clients can be invited into a virtual structure before it has been built to approve the plans. 3D models of equipment can be exploded to show their constituents parts and the relationship of those parts to one another, deepening understanding of complex machinery.

Abstract concepts presented in 3D can greatly aid education; for example, calculus equations can be modified by changing the variables, and the 3D graph on which they are presented can be rotated and viewed from multiple angles, engaging our natural senses in grasping what the equation represents.

Rare and ancient artifacts that are housed in restricted locations can be held and examined closely, and cities and buildings that no longer exist can be explored to provide a deeper understanding of the real-life experience of them. As we break free from what Tony Parisi calls the “tyranny of the rectangle” – the limited view, flat mode in which we have been accustomed to encounter media and images – we can fill the virtual world with 3D digital objects and visit previously inaccessible environments. 

File Formats 

There are a wide variety of file formats that are used to share 3D models. Some of these formats are particularly well suited to XR collaboration use cases. A number of the XR collaboration tools listed in the XR Collaboration Interactive Platform Directory allow users to directly import 3D models from third-party asset stores or from the user's local device. Pay attention to the specific file formats that are supported by the tools you select. There is a wide variety of content variation in 3D file formats, therefore it may take some experimentation to get an asset imported.

In addition to the format itself, there may be other restrictions or requirements such as the maximum number of polygons, the maximum number of associated textures, and the total number of textures. You should not start by assuming you can import a model that has hundreds of thousands or millions of polygons!

Some good starting guidelines are to use models that:

  • Have a maximum of 100K polygons
  • Use textures that are less than 1024x1024 in resolution
  • Use less than 10 textures

Next, let's examine the most popular 3D file formats so you can understand more about them and their purpose.


OBJ

The .OBJ file format is a simple 3D file format that contains only 3D geometry data. They are historically a common method for sharing 3D objects – most 3D creation tools will support exporting a 3D model into this format. .OBJ files can also contain references to supporting .MTL files which contain "material libraries" – descriptions on how to render the surface of the 3D model.

Although commonplace and well supported, .OBJ files are an older format and do not support many modern surface rendering features and other things such as animation.

Stanford "Bunny" model in .OBJ format.
Stanford "Bunny" model in .OBJ format.

DAE / COLLADA

The .DAE (or COLLADA) file format is perhaps the most popular 3D model interchange format in existence. It was standardized and open sourced over a decade ago. Most popular 3D creation tools support importing and exporting COLLADA files.

One nice thing about COLLADA files is that you can describe the physics associated with objects, which can enable more sophisticated interactions with them. COLLADA files also support more modern rendering techniques and can produce more photorealistic results.


Bunny model rendered in COLLADA format (from TurboSquid)

FBX

The .FBX file format has been around since 2006 and was popularized by Autodesk.

Why is this important - animation, Unity support, etc.

The .FBX format supports 3D models, scene framework, lighting, and animations, among others. It is good for complex models, fast to write and read, and compatible with most tools.

Animated frog in FBX format (from TurboSquid)
Animated tree frog in FBX format (from TurboSquid)

GLTF / GLB

The glTF file format is a relatively modern standard that is used to describe 3D model geometry, appearance, scene graph hierarchy, and animation. There are two variations of this file format: .gLTF, which is a format that may reference external supporting files containing extra data such as textures, and .GLB which is a self-contained binary format where all of the data needed is in a single place.

The glTF format was originally created by the same group that designed the COLLADA file format, and it is currently one of the most popular ways to deliver 3D assets for use in augmented reality tools.

glTF render of the Stanford Bunny model.
glTF render of the Stanford Bunny model (available on SketchFab)

USD / USDZ

The .USD file format was introduced in recent years as an even more modern interchange format for 3D graphics data. Co-designed by Apple and Pixar, .USDZ files are basically uncompressed .ZIP files containing .USD files and other asset files needed to render the 3D content described within. Apple standardized support for USDZ files starting with iOS 12 and many iOS XR collaboration applications can import them.

CAD / Large 3D Models

There is a long history of file formats used for stored CAD (Computer Aided Design) data. Probably the most common one is the .DWG format, which is a widely used format for CAD drawings.

There are many other formats used to create multi-million polygon models in CAD/CAM applications; for example, CATIA, NX, SolidWorks, Creo, STEP, and IGES. Look carefully at the XR collaboration platform you are planning to use to understand the large 3D model formats they support. You may find a need to convert 3D assets from the tool used to create it to a format compatible with your XR collaboration tool. There are a number of conversion systems available for this purpose – for example: https://www.pixyz-software.com

Creating Your Own 3D Models

The advent of depth cameras and LiDAR support on mobile phones makes it much easier to create 3D objects by scanning real world objects.

Samsung introduced the 3D Scanner app on Galaxy Note10+ phones which allowed you to take a 360 degree snapshot of an object and turn it into an animated GIF. On newer phones, you can get even better results in scanning and export to a .ZIP file which contains a .glTF format object. You can also export .OBJ files.

Apple released LiDAR-enabled iPad and iPhones over the past year. These can be used to create 3D point clouds and 3D models of real world locations and objects. Some XR collaboration tools can now directly import LiDAR assets!


Acquiring Professional 3D Models

Most people are not familiar with using 3D modeling and creation tools. As a result, a number of marketplaces have developed, which enables access to free and paid models. These platforms provide powerful search, filtering, and sorting tools to facilitate you finding the models – especially useful to find models which are compatible with the XR collaboration platform that you are using.

Let's take a look at a few of the more mature marketplaces.

SketchFab

SketchFab provides an online and mobile platform where visitors can browse, rate, download, or buy user-generated 3D models.

SketchFab store catalog showing freely downloadable images.

TurboSquid

TurboSquid has been around for 20 years as one of the original marketplaces for 3D models. They were recently acquired by ShutterStock and will probably grow significantly as a result. They have a highly searchable database of models, including a file format filter right on their homepage.


CGTrader

CGTrader has also been around quite a long time and has a large library of 3D models to search through.