STL

STL is a file format that describes the outer surface of an object as a set of connected triangles. The name comes from stereolithography, the printing process it was first made for. The file holds only triangle vertex coordinates and their facing direction; there is no color, texture, material or unit information. It can be saved as text (ASCII) or binary.

STL and 3D printing

When a scale model or prototype is going to be printed, the geometry is usually handed to a slicer as STL. The slicer cuts the surface into layers and works out the path the printer will follow. What matters here is not how the model looks but whether it is closed and error-free: holes, flipped faces, self-intersecting parts and single faces with no thickness all cause failed prints.

Preparing an architectural model for STL

• A model built for rendering rarely prints as is; single-face glazing and thin details need real thickness.
• Scale is not stored in the file, so note the export unit and pick the same one in the slicer.
• Details too small to read at model scale should be simplified, or they simply disappear in the print.
• Large models are printed in pieces, which means splitting the model into sensible parts from the start.

STL is not a rendering format. But if the same project needs both images and a physical model, keeping separate export settings for each is a good habit.