Words you will meet

A plain-language glossary: STEP, mesh, triangle, GLB, instancing, decimation, WebGPU, virtual environment and the other terms these pages use.

You do not need to learn these before you start. Come back to this page when a word is new.

Files and formats

CAD: Computer-aided design. The programs engineers use to design real objects, such as SolidWorks or NX.
STEP (.step, .stp): A file format for exchanging CAD designs between programs. It stores exact surfaces, part names, colours and how the parts fit together.
GLB: A compact 3D file made of triangles, with colours and part names inside one file. Browsers and most 3D programs can open it. This is the format MeshOptimiser writes by default.
glTF: The same format as GLB, written as readable text. The app’s own format sheet describes it as the same capabilities, larger.
FBX, OBJ, STL, PLY, USDZ, 3MF: Other 3D file formats. File formats says what each one is for.
XCAF: The part of a STEP file that holds names, colours and the assembly tree. You see the word in the import settings.

Part: One piece of the model: a bolt, a cover, a bracket. Each part has a row in the parts tree.
Assembly: A model made of many parts, often arranged in groups inside groups.
Group: A folder in the parts tree. It holds parts or other groups.
Mesh: The surface of a part, built from many small flat triangles.
Triangle (tri): The smallest piece of a mesh. The app counts everything in triangles: more triangles mean a heavier model.
Polygon: Another word for the flat pieces of a mesh. In this app it means the same as triangle.
Vertex: A corner point of a triangle. The plural is vertices.
Normal: A hidden arrow on the surface that tells the light which way the surface faces. Wrong normals make a part look oddly shaded.
Bounding box (bbox): The smallest box that a part fits inside. The app uses it to measure how big a part is.
Origin and pivot: The origin is the point 0,0,0 of the scene. A pivot is the point a part turns around.
Material: What a surface looks like: its colour and how shiny or metallic it is. Many parts can share one material.

Tessellation: Turning the exact curved surfaces of a CAD file into triangles. Finer tessellation means smoother curves and more triangles.
Instancing: Storing one mesh for a shape that repeats, plus the list of places where it sits. 400 identical bolts become one bolt and 400 positions.
Decimation: Removing triangles from a mesh while keeping its overall shape. It is lossy: detail that is removed does not come back, except through undo.
Lossy: An action that throws detail away to save size.
Compression: Packing the same data into a smaller file. Meshopt and Draco are two methods for 3D files.
Meshopt: A compression method for GLB files. The converter applies it through a separate tool called gltfpack, when that tool is installed.
Draco: Another compression method for GLB files. It is a switch in the Export window.
Scene: Everything in one tab of the app: the parts, their materials, the camera and the undo history.
BOM: Bill of materials: a parts list. The CSV export writes one.

Viewport: The large 3D view in the middle of the window.
Parts tree: The list of parts and groups in the left sidebar.
Gizmo: The coloured arrows, rings or handles that appear on a selected part, for moving, rotating or scaling it.
Orbit, pan, zoom: Turning the view around the model, sliding it sideways, and moving closer or further away.
Isolate: Showing only the selected parts and hiding everything else for a moment.
Draw call: One instruction to the graphics card to draw something. Fewer draw calls usually mean a smoother view. The optimisation report counts them.

Python: A programming language. The converter and the small local server are written in it, so Python has to be installed.
Virtual environment (.venv): A private folder of Python add-ons that belongs to this app only. The launcher creates it inside the app folder the first time, so nothing else on your computer is changed.
Terminal: A window where you type commands. On Windows it is called Command Prompt or PowerShell, on macOS it is called Terminal.
Local server: A small program on your own computer that hands the app’s pages to your browser. Its address is normally http://localhost:4242. Localhost means this computer.
PATH: The list of folders where your computer looks for programs. Python has to be on it for the launcher to find it.
WebGPU: The modern way for a browser to use the graphics card. The viewer uses it when the browser has it.
WebGL2: An older way to do the same. The viewer uses it when WebGPU is not available.
Installing the app (PWA): Chrome and Edge can add a web page to your desktop and Start menu as if it were a program. A page that supports this is called a progressive web app, or PWA.