STL file

In recent years, new technologies have emerged, such as additive manufacturing processes (3D printing) and digital CAD/CAM (Computer Aided Design and Manufacturing) chains for the healthcare sector. All these technologies traditionally rely on the STL file format to model the geometric information of parts or shapes. This digital modeling and file format was historically developed by 3D Systems in 1986. This 3D file format contains only the minimum necessary to describe the 3D model, making it compact and easy to use. What's more, the ease with which the STL model of the part can be computationally decomposed into a set of simple elementary layers, known as "strata", makes it a suitable format for stereolithography. Over the past few years, this file has seen a resurgence in interest and an increase in its use/handling by healthcare professionals and industrialists alike, as well as by private individuals.

Several interpretations are commonly associated with the acronym STL. These include STereoLithography, Surface Tessellation Language and Standard Triangle Language. Whichever acronym is chosen, the virtual digital data associated with the digital model is structured, organized and grouped in its own way, within a file and characterized by the file extension given to computer files (in our case .stl).

The STL file extension is based on a polyhedral surface model of the object it represents, also known as a mesh. It is therefore a skin with no thickness and no material (filling) inside. Only the direction of the material is indicated. It also has no metadata (color, texture...) or other parameters typical of a computer-aided design model (material, thickness, parameters, design entities...), which is one of the main criticisms made by developers of additive manufacturing (AM) solutions.

The STL format is one of the so-called "neutral" formats, offering interoperability between different CAD (Computer Aided Design) software and/or an intermediate format for conversion between two proprietary (native) CAD formats.

This article covers the essential concepts involved in structuring an STL file. Firstly, it describes the important information required for its use. Next, methods for calculating the area of an STL mesh and the volume included within it are described. Common defects and key criteria for assessing the quality of an STL mesh are detailed. Finally, alternatives to the disadvantages of the STL file format are proposed.

At the end of the article, readers will find a glossary and a table of acronyms.