Mesh Generation Workshop 2 Planning

[SorooshMani-NOAA]

We'd like to hold another meeting/workshop to share ideas about mesh generation and mesh generation tools for coastal modeling purposes. We opened this discussion to gather all the ideas for the workshop planning.

[SorooshMani-NOAA]

@WPringle @tomsail @pmav99 @brey had a brief meeting on 3/19 to come up with some initial ideas. As opposed to last workshop/meeting (https://github.com/oceanmodeling/seamesh/tree/main/presentations) where we didn't have a tangible outcome, this time we'd like to be able to come up with ideas for everyone involved to start developing and contributing.

For planning this meeting 3 main questions need to be answered:

• Who's the audience?
• How long the meeting is (half a day, full day, multiple days)?
• What does the meeting focus on?

Who

I think it makes more sense if this time we only include willing modelers, i.e. users of the meshing tool that would also contribute to its development either in terms of code development or ideas and feature list. We already have a good idea of what meshing engines are out there and what their capabilities are, so there's no need to involve mesh engine (triangulation) developers.

Topics

The following items need to be considered/discussed in the workshop:

• Existing tools' features and missing pieces
• Solver support (e.g. SCHISM, WW3, MPAS, etc.)
• List and pros and cons of each engine
  • Also support for wrapping multiple engines
• Wishlist and features such as
  • Global vs regional mesh
  • Euclidean vs Ellipsoid meshing
  • Projection/CRS handling
  • Feature extraction
  • Quality metrics and mesh post processing
• Development
  • Should we start development from scratch or continue on an existing tool
  • Modular system
    • Should DEM processing be separate from mesh package?
  • Avoiding one package does all idea (e.g. pyPoseidon)
  • Internal mesh representation
  • IO can be handed off (plugins, etc.) to other packages (e.g. meshio)
• Usability
  • User inputs
  • Use cases

Format

Depending on the amount of time we dedicate to the workshop, we might be able to tackle discussing both a list of existing tools and workflows (at a practical hands-on level) as well as developing wishlist for where to go next.

Ideas:

• Start by presenting existing tools
• The presenters also prepare a list of features they use, and wishlist of what they would like to see (bullet points)
• After all presentations we gather all lists and start cataloging features, what feature exists where and whether this is a good candidate to move to the target repo
• We can prepare a code base for the workshop and then discuss evolving it as a part of workshop.

[tomsail]

Hi all,

I'll initiate the discussion with our use case at the JRC:
we generate global meshes for global surge models. The models we use are:

• TELEMAC
• SCHISM

We have encapsulated 3 meshers inside pyPoseidon:

• jigsaw
• gmsh
• oceanmesh

Here are the pro/cons for each mesher:

Tool	Pros	Cons
Jigsaw	Very efficient in performance Quality of the mesh is really good	License not compatible with GPL
Gmsh	CLI & Python wrapper Possibility to define local scale function on the boundary independently Support for multiple scaling Large active community with extensive documentation GPL license	Takes time to run for complex and big coastlines
OceanMesh	Very modular (all sizing functions can be switch on/off) Distance Feature Bathy gradient Wavelength Thalweg Good quality meshes Should work for different projections	Small community on Python

Metrics / Wish-list

To analyse and correct the mesh, the following metrics would be nice to have to prepare the mesh (depending on the solver you use)

• Equilateralness
• Max neighbor node number
• Max size or area
• CFL condition

TELEMAC built-in check-mesh.py routine has also the following checks that could be interesting for other models:

• Circle_ratio
• Check_angle
• Over-constrained nodes
• Orthogonality

pyPoseidon has also a few check/correction implemented:

• Check the mesh against the coastlines
• A CCW check (triangle orientation)
• Triangles crossing the IDL (international date line)

One pager presented in the last OceanModeling meeting with useful links
OM_management_meeting_20240606.pdf

Other software with interesting features:

• BlueKenue for generating, editing, visualising Selafin (TELEMAC format) files.
• MeshTools (by @daoum , @nicogodet and @ccoulet): QGIS plugin for visualizing mesh quality (Equilateralness / Max number of neighbors, Max size or area). This one could be interesting for you also @AliS-Noaa

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Global model implementations

• pyposeidon - oceanmesh > reproducible versions available at: https://github.com/seareport/seareport_models
• pyposeidon - gmsh > example available at https://github.com/ec-jrc/pyPoseidon/blob/master/Tutorial/GLOBAL.ipynb
• jigsaw (for WW3 models) https://github.com/NOAA-EMC/WW3-tools/tree/develop/unst_msh_gen
• seamsh example: https://git.immc.ucl.ac.be/jlambrechts/seamsh/-/blob/master/examples/6-stereographics.py?ref_type=heads