Coastline simplification for mesh generation

[brey]

When trying to create global meshes for high resolution coastal simulations, defining the coastlines in a consistent manner is important for

• Improved coastline resolution accuracy
• Be able to control resolution per region (e.g. resolution in the Black sea straits might need to be smaller than e.g. some ocean coast)
• Topographically validity
• "Fast" mesh generation (coastlines with the "appropriate" number of nodes for the resolution)
• High quality mesh generation

The following requirements should also be met:

• Transparency
• Reproducibility
• "Stay on sea" - The elements are always wet

Using the Open Street Map coastlines poses the following problems:

• Too big, 800k polygons vs 180k for "Full" GSHHG.
• Too detailed, 75 million nodes vs 10 million nodes for GSHHG.
• no published versions. You need to handle versioning yourself.
• There is no consistency when dealing with lagoons and estuaries.

We are working on a solution that would provide the following characteristics:

• splitting the world in regions, to address different resolution/projection requirements.
• island grouping, to keep resolution above a threshold.
• Predefined edge size, for fixing coastal resolution.

This way, the pre-processing is done transparently and the meshing process doesn't affect the coastline representation.

There are many ways to handle some specific aspects of this process. We would like to address here these issues.