Function for periodic global grid to non-periodic

[veenstrajelmer]

Copy x=-180 nodes to x=180 and update face/edge topology.

In case of periodic grid, conversion to non-periodic is necessary for:

• rasterizing
• interpolation
• plotting
• regridding

All these features fail if there are "around the back" cells/faces

Test data is available at p:\1230882-emodnet_hrsm\GTSMv5.0\runs\reference_GTSMv4.1_wiCA_2.23.08_mf4\output_small\

Partition 0005 also goes around the back, so testing with only 1 partition is also possible.

[Huite]

For plotting: an attribute (or property or something) denoting it's periodic would be useful. In that case, there's no need to create a whole new topology: just special case it for the plotting.

For e.g. plotting in QGIS -- which doesn't support periodic grids -- you'd still need to convert.

[Huite]

Periodic arguably has a more general meaning that what we describe here: https://en.wikipedia.org/wiki/Periodic_boundary_conditions

Periodic boundary conditions (PBCs) are a set of boundary conditions which are often chosen for approximating a large (infinite) system by using a small part called a unit cell. PBCs are often used in computer simulations and mathematical models. Periodic boundary conditions (PBCs) are a set of boundary conditions which are often chosen for approximating a large (infinite) system by using a small part called a unit cell. PBCs are often used in computer simulations and mathematical models.

However, the logic required to create such a grid is exactly identical to the one required for this global grid. If we have a grid which runs from x=0 to x=5, but we want a periodic simulation to simulate an infinite domain, we would similarly connect the left side to the right by substituting the rightmost face nodes with those on the left.

• to_periodic would substitute x=5 with x=0.
• to_nonperiodic would substitute the rightmost x=0 with x=5, given xmax=5.0 as an argument

I think the spherical cases can be reasonably seen as a special case where the domain is finite.

Although to properly implement it, an optional ymax argument should also be introduced, and xmax should be made optional as well.