pygmt.grdfill: Interpolate across holes in a grid

[seisman]

This is the central issue to track the implementation of the pygmt.grdfill method.

• GMT doc: https://docs.generic-mapping-tools.org/6.5/grdfill.html
• PyGMT doc: https://www.pygmt.org/dev/api/generated/pygmt.grdfill.html
• GMT.jl doc: https://www.generic-mapping-tools.org/GMTjl_doc/documentation/modules/grdfill/

GMT options

Checked: Implemented; Unchecked: To be implemented/discussed; Strikethrough: Won't implement.

• <ingrid> Wrap grdfill #1276
• -Ac|g|n|s[<arg>]
• -L[p]
• -G<outgrid> Wrap grdfill #1276
• -N<value>: no_data
• -R
• -V
• -f
• --PAR=value: Use pygmt.config

[seisman]

Here are my thoughts on finalizing the wrapper.

-N

This option has different long names across the GMT ecosystem.

• PyGMT: aliased to no_data. [Need to note that common option -d is aliased to nodata]
• GMT.jl: aliased to nodata or hole
• GMT: aliased to hole or hole_value

This option "sets the node value used to identify a point as a member of a hole [Default is NaN].". Personally, I feel hole is a better name than no_data.

-A

This option specifie the hole-filling algorithm to use. Currently it's aliased to mode and can be used like (please refer to the docs for the actual meanings of these arguments):

• mode="c100"
• mode="ganother_grid.nc"
• mode="n0.5"
• mode="s0.3"

The syntax is not Pythonic, since we have to specify numbers in a string, and for the mode="ganother_grid.nc" case, the "another grid" must be a string, and can't accept a xarray.DataArray object.

In my mind, there are two possible ways to make it more Pythonic:

1. Two parameters mode and value.

   • mode specifies the filling method. Valid values are "constant", "grid", "neighbor", "spline"
   • value has different meanings for different filling methods, e.g., value=100, value="another_grid.nc", value=0.5, value=0.3

2. Four exclusive parameters

   • constantfill=100
   • gridfill="anonter_grid.nc" or gridfill=xrgrid
   • neighborfill=True or neighborfill=0.5: 0.5 is the search radius, and True means the default radius
   • splinefill=True/splinefill=0.3: 0.3 is the spline tension, True means no tension.

I prefer the 2nd option.

What do others think?