Words you will meet

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.

What a model is made of

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 (n-gon)

A flat face with any number of corners. Several triangles that lie in one plane can be joined into one polygon. Triangulation does that, and turns polygons back into triangles. In Edit mesh, two triangles that make a four-sided shape count as one polygon.

Vertex

A corner point of a triangle. The plural is vertices. In Edit mesh it is called a point.

Edge

The line between two points where two polygons meet, or where a surface ends.

Loop

A row of polygons or edges that runs round a part, like a ring round a tube. Edit mesh picks one with a double-click.

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.

What the app does to a model

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 command-line converter applies it through a separate tool called gltfpack, when that tool is installed. The Export window has a Meshopt switch of its own, which needs no extra tool.

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.

The screen

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. In Edit mesh it moves the picked points, edges or polygons instead.

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.

Edit mesh

A mode in which you pick and change the points, edges and polygons of a part instead of whole parts. See Edit mesh.

Bake geo

A button in Properties that turns a library shape into an ordinary mesh. The shape’s numbers go, and the mesh tools work on it. See The parts library.

Align and spread

Lining parts up on one side or the middle along an axis, or spacing them evenly. See Align parts.

Dissolve, weld

Two Edit mesh tools. Dissolve takes pieces out and closes the surface over them. Weld makes several points one.

Shortcut profile

A named set of keys that you changed. The app’s own keys are the Default profile, which cannot be changed. See Keyboard shortcuts.

Draw call

One instruction to the graphics card to draw something. Fewer draw calls usually mean a smoother view. The optimisation report counts them.

The technical side

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.