isl-org/Open3D ? reverse-engineered prompt

Build me a modern open source library for working with 3D data.

I want it to handle the common things people do with point clouds and meshes, like loading data, cleaning it up, aligning shapes, reconstructing surfaces, and visualizing results in a simple 3D viewer. It should be usable from both C++ and Python, and the Python side should feel easy for quick experiments and notebooks.

Please also include GPU acceleration where it makes sense, basic support for physically based rendering, and a few small examples that show the main workflows end to end. If possible, make the project easy to install on the main desktop platforms, and add a simple command line demo so I can verify it works right away.

If you need to check current build or packaging details, look up the latest docs online and follow those patterns.