This Python program provides a simple, fast, and robust way to visually compare 3d files such as STL, OBJ, 3MF, and STEP. The unchanged parts of the objects are shown in gray, while the changed parts are shown in contrasting colors that stand out, illustrated by the following example.

In this example most of the lens clamp is unchanged and is displayed in gray, while the differing parts are displayed in red for one file and green for the other file: in the red file the diameter is smaller, while in the green file the base is longer, and the threaded hole has moved.

Quick start

git clone https://github.com/bdlucas1/diff3d
cd diff3d
pip install -r requirements.txt
python diff3d.py examples/lens-clamp-A.stl examples/lens-clamp-B.stl

The diff3d command may take up to about a minute to run the first time while it loads and compiles the supporting packages, but after that the startup time will be very quick.

You can drag the displayed object to rotate it, use the mouse wheel to zoom, and shift-drag to pan.

The second file is optional, in which case the first file will simply be displayed without diffs. This allows the tool to be used as a simple 3d file viewer in addition to its primary function.

If there is enough interest I'll look into publishing this as a pip-installable package.

Supported platforms, file formats, and object types

I have only tested this on MacOS with Python 3.12 and 3.13. If you have information about the status of other platforms please let me know.

Out of the box diff3d supports STL, OBJ, and 3MF files. Support for a number of additional file types is available by installing meshio, and support for STEP files can be enabled by installing build123d.

Unlike other tools that do 3d diffs by using 3d boolean operations like intersection and difference, this tool is robust and is not limited to manifold (closed surface) meshes, but can diff anything that can be rendered, including open surfaces, curves, and points.

Color schemes

Three color schemes designed to be colorblind-friendly are provided. (This is based on information from https://davidmathlogic.com/colorblind, and I have not verified this. If you have information to add please contact me by opening an issue on github.)

You can choose a scheme using the -s or --scheme option. The above schemes are named "1", "2", and "3" respectively.

API

The diff3d module provides a simple API if you want to integrate it into your own program. See the code for details.

• diff3d.from_files opens a window displaying the diff between two files

• diff3d.diff opens a window displaying the diff between two pyvista objects.

• If you are using a different mesh or CAD package, if you can obtain point and triangle arrays, you can convert them to pyvista objects using pyvista.PolyData.from_regular_faces