feat: add optional coastline layer to 3D visualization

[Prince637-boo]

Summary of the changes :

This PR introduces an optional coastline layer for the 3D interactive visualization using Plotly.

Created a new geo_data.py module containing a simplified, low-resolution dataset of global coastlines to ensure the package remains lightweight.

Added a new add_coastlines boolean parameter to the render_with_plotly function.

Implemented _build_coastline_trace to convert geographic coordinates into 3D Cartesian space on a sphere, using efficient line-batching (None-separated arrays) to optimize performance.

Integrated the coastline layer within the concentric layout mode.

Motivation and context:

Visualizing weather model graphs on a blank sphere can make it difficult for users to orient themselves geographically. Adding a coastline background provides essential spatial context, allowing users to immediately identify which parts of the globe the graph nodes and edges represent. This was inspired by discussions in #118 regarding the need for better spatial cues in 3D plots.

Dependencies:
No new external dependencies were added. The feature uses existing plotly, numpy, and networkx requirements.
Issue Link

Solves #118 (or "Relates to #118" if the issue is still open for other 3D tasks)
Type of change

[ ] 🐛 Bug fix

[x] ✨ New feature

[ ] 💥 Breaking change

[ ] 📖 Documentation

Checklist before requesting a review

[x] My branch is up-to-date with the target branch

[x] I have performed a self-review of my code

[x] For any new/modified functions/classes I have added docstrings

[x] I have placed in-line comments to clarify the intent

[x] I have updated the documentation (docstrings)

[x] I have added tests that prove my feature works

[x] I have given the PR a name: feat: add optional coastline layer to 3D visualization

[x] I have requested a reviewer

[Prince637-boo]

Visual Representation:

Here is a preview of the new coastline layer enabled on a concentric 3D layout. The coastlines are rendered slightly below the grid level (radius ~0.99) to provide context without obstructing the data points.

[yuvraajnarula]

# Visual Representation: Here is a preview of the new coastline layer enabled on a concentric 3D layout. The coastlines are rendered slightly below the grid level (radius ~0.99) to provide context without obstructing the data points.

@Prince637-boo
Thank you for putting this together! 🙌

Since #118 already includes a basic add_coastlines parameter and the concentric layout, your coastline data and modularisation would be a perfect enhancement. To keep things clean, I’d suggest we either:

• Merge feat: add 3D interactive graph visualisation with Plotly #118 first, then rebase this PR on top of it, or
• If you’re comfortable, we can directly add your coastline improvements to feat: add 3D interactive graph visualisation with Plotly #118 (with proper credit) and close feat: add optional coastline layer to 3D visualization #126 as a duplicate.

Either way, I’m happy to help coordinate and review. Let me know what works best for you. Great to see the 3D visualisation growing with community input!

[Prince637-boo]

Hi @yuvraajnarula,

That's a great idea! I'm perfectly fine with the second option.

Please feel free to integrate my coastline improvements and the geo_data.py module directly into #118. I think it’s much more efficient to have a single, solid PR for the 3D visualization.

I'm happy to help with any adjustments needed to make the integration smooth. Once you’ve moved the code, I’ll close #126.

Thanks for the warm welcome and for the proper credit, I'm glad to contribute to this!

[Prince637-boo]

Closing this as the features have been integrated into #118.