FVCOM Grid Generation

Utilities and examples for generating 2D Gmsh meshes, including adaptive coastal meshes suitable for FVCOM-style workflows.

What is in this repo

• basic_mesh_example.py: builds a simple rectangular mesh and writes rectangle_mesh.msh.
• adaptive_mesh_example.py: builds a rectangle with spatially varying target element size and writes adaptive_mesh.msh.
• coastal_bathy_adaptive_mesh.py: builds a coastal ocean mesh with refinement near shoreline and shallow bathymetry.
• load_mesh.py: loads a .msh file, reconstructs coordinates, and plots the mesh over a basemap.

Requirements

• Python 3.10+
• Internet access for first-time coastal data downloads
• Gmsh desktop application (https://gmsh.info/) if you want to open meshes in the Gmsh GUI interface

Install Python dependencies:

python -m pip install -r requirements.txt

Quick start

Run the simple examples:

python basic_mesh_example.py
python adaptive_mesh_example.py

These produce:

• rectangle_mesh.msh
• adaptive_mesh.msh

Coastal adaptive mesh generation

Run interactively and enter coordinates at prompts (press Enter after each value):

python coastal_bathy_adaptive_mesh.py

Prompt sequence:

• Enter lat-min:
• Enter lat-max:
• Enter lon-min:
• Enter lon-max:

You can also pass coordinates directly with flags:

python coastal_bathy_adaptive_mesh.py --lat-min 44.8 --lat-max 52.0 --lon-min -129.0 --lon-max -121.0

Optional arguments:

• --output-mesh: output mesh filename (default: coastal_adaptive_mesh.msh)
• --cache-dir: cache directory for downloaded data (default: mesh_cache)
• --show-gui: open the Gmsh GUI after mesh generation

Outputs:

• coastal_adaptive_mesh.msh
• coastal_adaptive_mesh.json (projection sidecar used for back-projection in plotting)
• Download/cache files under mesh_cache/

Visualize a generated mesh

By default, load_mesh.py reads coastal_adaptive_mesh.msh and saves a map image:

python load_mesh.py

Output:

• mesh_map.png

Notes

• The first coastal run downloads global bathymetry and Natural Earth land polygons; later runs reuse cached files.
• If plotting a projected coastal mesh, keep the .json sidecar next to the .msh file so coordinates can be converted back to lon/lat.

Attribution

• Parts of the bathymetry/coastal mesh workflow in this project were adapted from: https://github.com/emmashie/model-agent/blob/main/agents/llm_grid_agent.py
• Please refer to the upstream repository for original context, updates, and licensing details.