Kate Murray is Digital Projects Coordinator, Leader of Sustainability of Digital Formats and FADGI Audiovisual Working Group at the Library of Congress in the USA
3D content, both digitized and born-digital, continues to be an area of focus across the Library of Congress. Last year on the #WDPD blog, we focused on a recap of the Born to Be 3D: Digital Stewardship of Intrinsic 3D Data (#B2B3D) small group forum to discuss stewardship of born digital 3D data. This year on the Sustainability of Digital Formats website, we’re diving a bit more in depth to explore file formats for 3D for scanning, printing and modeling.
Some of recent additions include entries on Extensible 3D (X3D), standardized in ISO/IEC 19776open standard and often used for 2D and 3D graphics, 3D viewers, animation, computer assisted design, as well as printing. Universal 3D (U3D) is a binary format standardized in ECMA-363 and supports for downstream 3D CAD repurposing and visualization, useful for many mainstream business applications. Polygon File Format (PLY) on the other hand is a simpler format for describing an object as a polygonal model. It is often used to store the output from a 3D scanner or other process used to generate a point cloud or polygon mesh model of the surface of a physical artifact; 3D models are often shared for re-use in the PLY format. The Wavefront OBJ format defines the 3D geometry for the surface of one or more object surfaces using polygonal meshes or using freeform curves and surfaces. Its companion format Wavefront Material Template Library (MTL) File Format is an ASCII-based file that describes surface appearance properties to be applied to polygonal facets or freeform curved patches defined in an OBJ file. In short, the MTL file is a "library" that can contain one or more named material definitions, each of which can specify color, texture, and reflection characteristics. The STL (STereoLithography) File Format is a simple, openly documented format for describing the surface of an object as a triangular mesh. Since its introduction in the late 1980s, STL has become a de facto standard for rapid prototyping and 3D printing. Graphics Language (GL) Transmission Format (glTF) format is structurally a collection of related files, comprising a JSON file and supporting external data file used for the for the transmission and loading of 3D content.
One of the main features of Sustainability of Digital Formats is not only the investigation and documentation of a format’s technical characteristics but also an analysis of both sustainability as well as quality and functionality factors. Q&F factors assess a format in relation to functional support for features and aspects that can affect the quality of content. For 3D content, we’ve adapted a set of criteria outlined by the National Center for Supercomputing Applications (NCSA) in An Overview of 3D Data Content, File Formats and Viewers, a technical report (ISDA08-002). According to this analysis, the key aspects of a 3D model are: geometry, appearance, scene, and animation.
Caption: 3D Model Formats Quality and Functionality Factors and definitions
3D is interactive by design so 3D formats are often so they may employ quality and functionality factors from multiple content categories. For example, the description for Scene Layer Package (SLPK) File Format container for Indexed 3D Scene Layer (I3S) used for 3D geospatial content includes not only the 3D Q&F factors but also includes support for software interfaces (Dataset) and support for GIS metadata (GIS Image and Datasets).
Comments are always welcome on our format descriptions and related content on the Sustainability of Digital Formats website. Incidentally, this year the website reaches a milestone 15 year anniversary! The site contains over 460 format descriptions across arrange of content areas and attracts an average of 40,000 unique visitors a month. Format descriptions are available in HTML as well as XML for individual or bulk download.
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