IceBin Regridding

IceBin uses the techniques of conservative_regridding_ to produce regridding matrices for GCMs employing elevation classes. IceBin requires three grids to be defined:

• A = atmosphere grid, used by the GCM.
• I = ice grid, a high-resolution grid for an ice-covered region of the globe. It may be defined in spherical or Cartesian geometry; if Cartesian, then overlap matrices will be computed with the atmosphere grid by projecting the atmosphere grid to the same Cartesian space. Every grid cell in the ice grid has a single elevation; and must be either 100% ice-covered or 100% ice free. If the GCM is coupled with a dynamic ice model, the ice model is run on this grid.
• E = elevation grid, an intermediate-resolution grid, derived from the atmosphere and ice grids. The land/ice surface model is run on this grid. See Fischer and Nowicki, 2014 <https://pubs.giss.nasa.gov/abs/fi03200y.html> for more information on how this grid, and its basis functions, are derived and used.

Give these three grids, IceBin generates the six regridding matrices between them, scaled or unscaled.