pygmt.grdpaste: Join two grids along their common edge

[Chuan1937]

pygmt.grdpaste: Join two grids along their common edge

Preview: https://pygmt-dev--4399.org.readthedocs.build/en/4399/api/generated/pygmt.grdpaste.html#pygmt.grdpaste

[seisman]

Also need to add it to doc/api/index.rst.

[Chuan1937]

Could you also please check the min and max values in the result?
Must use temporary files for xarray.DataArray inputs because virtualfile_in returns all zeros when handling grdpaste.

[seisman]

Could you also please check the min and max values in the result? Must use temporary files for xarray.DataArray inputs because virtualfile_in returns all zeros when handling grdpaste.

I think this points to an upstream GMT bug, which should be fixed.

[Chuan1937]

There are 4 cases: file in file out, file in xarray out, xarray in file out, xarray in xarray out. At least the first case works with gmt 6.6, right?

Yes, But test_grdpaste only include case 3, 4. Do I need to add case1,2?

[seisman]

There are 4 cases: file in file out, file in xarray out, xarray in file out, xarray in xarray out. At least the first case works with gmt 6.6, right?

Yes, But test_grdpaste only include case 3, 4. Do I need to add case1,2?

Yes please

[seisman]

Could you please add one more test with grid1 as file and grid2 as xr.dataarray？

[Chuan1937]

Could you please add one more test with grid1 as file and grid2 as xr.dataarray？

When the first input is a real file path and the second is a virtual file (from a DataArray), a GMT_GRID_READ_ERROR is raised. However, if the first input is a virtual file and the second is a real file, it works normally.

success:

def test_grdpaste_grid1_file_grid2_xarray(grid, grid_bottom):
    """
    Test grdpaste with grid1 as file input and grid2 as xarray input.
    """
    with GMTTempFile(suffix=".nc") as tmp1:
        grdcut(grid, region=[-53, -49, -19, -16], outgrid=tmp1.name)
        result = grdpaste(grid1=tmp1.name, grid2=grid_bottom)
        assert isinstance(result, xr.DataArray)
        assert result.shape == (6, 4)
        # Check that the result has the expected min and max values
        assert result.min().values == 345.5
        assert result.max().values == 886.0

failure:

def test_grdpaste_grid1_xarray_grid2_file(grid, grid_top):
    """
    Test grdpaste with grid1 as xarray input and grid2 as file input.
    """
    with GMTTempFile(suffix=".nc") as tmp2:
        grdcut(grid, region=[-53, -49, -22, -19], outgrid=tmp2.name)
        result = grdpaste(grid1=grid_top, grid2=tmp2.name)
        assert isinstance(result, xr.DataArray)
        assert result.shape == (6, 4)
        # Check that the result has the expected min and max values
        assert result.min().values == 345.5
        assert result.max().values == 886.0

A temporary workaround is to detect mixed inputs in PyGMT and load the files as DataArrays, making both inputs virtual files:

 if {kind1, kind2} == {"file", "grid"}:
            if kind1 == "file":
                grid1 = xr.load_dataarray(grid1, engine="gmt", raster_kind="grid")
            else:
                grid2 = xr.load_dataarray(grid2, engine="gmt", raster_kind="grid")

This may be an issue with upstream GMT. Should we use the workaround or report the problem to upstream?
@seisman