Specify which interpolation method to use during regridding.

Values are:

- BILINEAR = 0
- Bilinear interpolation. Destination value is a linear combination of the source values in the cell which contains the destination point. The weights for the linear combination are based on the distance of the destination point from each source value.
- PATCH = 1
- Higher-order patch recovery interpolation. Destination value is a weighted average of 2D polynomial patches constructed from cells surrounding the source cell which contains the destination point. This method typically results in better approximations to values and derivatives than bilinear. However, because of its larger stencil, it also results in a much larger interpolation matrix than the bilinear method.
- CONSERVE = 2
- First order conservative interpolation. Value of a destination cell is the weighted sum of the values of the source cells that it overlaps. The weights are determined by the amount the source cell overlaps the destination cell. This method will typically give less accurate approximations to values than the other interpolation methods, however, it will do a much better job preserving the integral of the value between the source and destination. This method requires the corner coordinate values to be provided in the Grid, and it currently only works for Fields created on the Grid center stagger (or the Mesh element location).