The command-line converter

The converter is a Python script, step2glb.py. The app runs it for you when you drop a STEP file on the window. You can also run it yourself in a terminal, for example to convert many files, or to use options the import window does not show.

You never need this page to use the app. It is here for when you want more control.

Before you start

1. Start the app once with its launcher, so the Python environment exists. See Start it the first time.
2. Open a terminal in the app folder. On Windows: open the folder in File Explorer, click the address bar, type cmd and press Enter. On macOS: open Terminal, type cd and a space, drag the app folder onto the window, and press Enter.
3. Switch on the app’s Python environment. This makes the command python use the add-ons the launcher installed. On Windows, type the first command below. On macOS, type the second.

Convert a file

Replace input.step with the path of your file. The result is written next to it, with the same name and the ending .glb. The terminal prints what the converter is doing.

Examples

python step2glb.py input.step --quality 0.2 --min-size 0.5

A finer tessellation, and parts smaller than 0.5% of the model left out.

python step2glb.py input.step --relative

Quality as a fraction of the size of each edge, so it does not depend on the file’s units.

python step2glb.py input.step --meshopt

Compress the result with gltfpack.

python step2glb.py input.step --simplify 0.5

Also halve the triangle count. Lossy.

python step2glb.py input.step --no-colors --no-instance

The plain reader: no colours, no instancing.

python step2glb.py input.step --out small.glb --target-tris 200000

Adjust the quality automatically until the result has at most 200,000 triangles.

python step2glb.py a.step b.step c.step

Convert several files, one after the other.

Input and output

input

One or more STEP, IGES or BREP files.

--out, -o

The file to write. Only with a single input file. Without it, the GLB is written next to the input.

--force

Convert again even if an output that is newer than the input already exists. Without it, the converter skips a file that was already converted with the same settings.

Mesh quality

--quality, -q

How closely the triangles follow the true surface (the linear deflection). Smaller is finer and heavier. The default is 0.5, in the units of the file, normally millimetres.

--relative

Reads --quality as a fraction of each edge’s own size (OpenCascade’s relative deflection) instead of an absolute distance: short edges get a finer mesh, long ones a coarser one.

--angular

The angular deflection, in radians: a second limit on how coarsely curved surfaces are cut into triangles. The default is 0.5, about 28.6°.

--tiers

Tessellate by part size. Give the two limits between small, medium and large parts, in percent of the size of the whole model, then a quality in millimetres and an angle in degrees for small, for medium and for large parts. For example --tiers 5,30:2,60:0.2,30:0.05,10.

--min-edge

The smallest triangle edge the mesher may make, in the units of the file. It stops tiny fillets and threads from filling up with slivers. The default, 0, is no limit.

--size-cap

A part’s quality is never coarser than this share of its own diagonal, so small round parts are not left polygonal. The default is 0.002 (0.2 %). 0 turns it off. It is ignored with --relative and --tiers.

--grid

Mesh curved faces along their own directions: a fillet in even strips, a curved panel in a grid, not a scatter of triangles. The import window calls it Even strips.

--no-surfaces

Leave out the parts that are surfaces only (open shells) and keep the solids.

--brep

Also write the CAD faces and the true CAD edges beside the GLB (<name>.glb.brep.json and .brep.bin), which the viewer uses for CAD edit.

--no-normals

Do not write the normals of the CAD surfaces into the GLB. The viewer then works out the shading from the triangles. Without this option the normals are written, which is what makes fillets blend smoothly into the faces beside them.

--swap-yz

Turn the model a quarter turn about the X axis, for a Z-up CAD file that should stand in a Y-up scene.

--min-size

Leave out parts whose size is below this percentage of the model’s diagonal. The default, 0, keeps everything.

Budgets

--target-tris

Adjust --quality automatically to land at or under this triangle count. The conversion is run again up to five times.

--target-size-mb

The same, for the size of the output file in megabytes. With both set, the tighter one wins.

Repeated parts

--no-instance

Do not collapse identical shapes into instances. According to the README, it only has an effect together with --no-colors.

--pca-instances

An experimental, more aggressive way to find repeated shapes. It can turn symmetric parts the wrong way.

Colours, names and the tree

--no-colors

Use the plain reader: geometry only, no colours, names or hierarchy. The fastest.

--force-colors

Always read colours, names and the hierarchy. Without this option, the converter skips them for files over 1 GB.

--no-shuo

Skip per-instance colour overrides. A big saving in time on assemblies with many repeated parts.

--no-layers

Skip the CAD layers. With them read, each part carries the names of its layers into the GLB, where the app shows them and selects by them.

--no-materials

Skip material information.

--no-step-names

Skip product names. Parts get generic names in the tree.

--no-step-props

Skip validation properties such as mass and area.

--props

Work out the volume and surface area of every solid. Slow on big files.

--split-colours

A body whose faces carry several colours becomes one piece per colour, open along the colour seams, instead of one body with several materials.

--no-extras

Do not write the CAD information (names, assembly path, colour, part number, layers, material, volume and area) into the GLB.

Compression and reduction

These options use gltfpack, a separate free tool that has to be installed and on your PATH. Without it they are skipped, with a warning.

--meshopt

Compress the GLB with Meshopt, for files roughly ten times smaller. This is on by default whenever gltfpack is found.

--no-meshopt

Switch that default off.

--quantize

Store positions, normals and texture coordinates as smaller numbers.

--simplify

Keep this fraction of the triangles, between 0 and 1. 0.5 halves the count. Sharp edges are preserved. Lossy. It switches Meshopt on.

Speed

--parallel

Use this many worker processes for building the meshes in the plain reader (see --no-colors). The default, 0, does one at a time.

--mesh-jobs

Use this many worker processes to mesh the parts when colours and names are read, which is the normal case. Without it the app chooses by the size of the model: under 5,000 CAD faces everything is meshed in one process, above that in up to eight processes, half the cores of the computer. 0 or 1 meshes in one process. It has no effect together with --brep or --split-colours.

Several files and levels of detail

--batch

Convert every STEP, IGES and BREP file in this folder with the options given, one process per file, so a file that fails does not stop the rest. It prints a table, writes batch-report.csv, and exits with 1 if any file failed. With --out, that is the folder the GLB files go to.

--recursive

With --batch: include the sub-folders.

--file-timeout

With --batch: give up on a file after this many seconds. The default, 0, is no limit.

--lod

Levels of detail as percentages of the triangles, for example --lod 100,50,25. The first level is written to <name>.glb, the others to <name>_lod1.glb, <name>_lod2.glb and so on. Cannot be combined with --simplify.

--lod-error

The error limit of the level-of-detail simplifier, as a fraction of each mesh’s size. The default is 0.01.

Without typing

The folder also holds step2glb.bat (Windows) and step2glb.command (macOS). Drag a STEP file onto one of them to convert it with the default settings, without opening the viewer.

Options of the server

The launcher starts serve.py. Started by hand, it takes these options:

--tab

Open the app in an ordinary browser tab instead of a window of its own.

--no-browser

Start the server and open nothing. Type the printed address into a browser yourself.

--open, -o

Open this file at start. Accepts STEP, IGES, BREP, GLB and glTF files. For a STEP file it asks about quality first.

--port

Use this port instead of 4242.

--keep-running

Keep the server running after its window is closed. Without it, a server that opened the window stops about ten seconds after the last window closes.

--exit-when-closed

Stop the server when its window is closed, also with --no-browser.