Add xugrid extension for TriMesh plots from unstructured grid data

[rsignell]

Holoviz folks, as you can tell, I made this with Claude Code, and I've been using it for the past few months for many applications. But I have no idea how well it's coded.

@Huite did give it a quick look and didn't raise any red flags.

There is discussion on the xugrid repo here: Deltares/xugrid#204 (comment)

Please let me know if there is anything else I can do -- I'd love to see trimesh supported by hvplot!

Summary

• Adds hvplot/xugrid.py — registers .hvplot on xugrid.UgridDataArray and xugrid.UgridDataset, enabling uda.hvplot.trimesh() for unstructured triangular mesh plots
• Extends HoloViewsConverter (converter.py) with a trimesh() method that supports rasterize=True, geo=True, tiles=, cmap=, etc.
• Extends hvPlot in plotting/core.py with the hvPlotXugrid subclass; _get_converter() extracts mesh topology (node coords, face-node connectivity) and stores it in kwds
• Defers face-to-node interpolation until after groupby slicing, so extra dimensions (time, sigma layers) become interactive widgets rather than requiring explicit selection
• Adds hvplot/tests/testxugrid.py with 243 lines of tests covering node-data, face-data, time/depth groupby, geo projection, and rasterization
• Includes two example notebooks (FVCOM_xugrid.ipynb, STOFS_xugrid.ipynb) demonstrating real-world FVCOM and STOFS coastal ocean model output

Usage

import hvplot.xugrid

# UgridDataArray with node data
uda.hvplot.trimesh(clim=(0, 2), cmap='viridis', rasterize=True, tiles='OSM', geo=True)

# Face data with time/depth sliders (auto groupby)
uda_3d.hvplot.trimesh(rasterize=True)  # sliders for time + siglay

Test plan

• pytest hvplot/tests/testxugrid.py — all tests pass
• Manual verification with FVCOM/STOFS example notebooks
• Confirm import hvplot.xugrid is a no-op (clean ImportError) when xugrid is not installed

🤖 Generated with Claude Code