Source code for pygmt.src.grdcut

"""
grdcut - Extract subregion from a grid.
"""

import xarray as xr
from pygmt.clib import Session
from pygmt.exceptions import GMTInvalidInput
from pygmt.helpers import (
    GMTTempFile,
    build_arg_string,
    data_kind,
    dummy_context,
    fmt_docstring,
    kwargs_to_strings,
    use_alias,
)


[docs]@fmt_docstring @use_alias( G="outgrid", R="region", J="projection", N="extend", S="circ_subregion", V="verbose", Z="z_subregion", ) @kwargs_to_strings(R="sequence") def grdcut(grid, **kwargs): r""" Extract subregion from a grid. Produce a new ``outgrid`` file which is a subregion of ``grid``. The subregion is specified with ``region``; the specified range must not exceed the range of ``grid`` (but see ``extend``). If in doubt, run :meth:`pygmt.grdinfo` to check range. Alternatively, define the subregion indirectly via a range check on the node values or via distances from a given point. Finally, you can give ``projection`` for oblique projections to determine the corresponding rectangular ``region`` that will give a grid that fully covers the oblique domain. Full option list at :gmt-docs:`grdcut.html` {aliases} Parameters ---------- grid : str or xarray.DataArray The file name of the input grid or the grid loaded as a DataArray. outgrid : str or None The name of the output netCDF file with extension .nc to store the grid in. {J} {R} extend : bool or int or float Allow grid to be extended if new ``region`` exceeds existing boundaries. Give a value to initialize nodes outside current region. circ_subregion : str *lon/lat/radius*\[\ *unit*\][**+n**]. Specify an origin (*lon* and *lat*) and *radius*; append a distance *unit* and we determine the corresponding rectangular region so that all grid nodes on or inside the circle are contained in the subset. If **+n** is appended we set all nodes outside the circle to NaN. z_subregion : str [*min/max*\][**+n**\|\ **N**\|\ **r**]. Determine a new rectangular region so that all nodes outside this region are also outside the given z-range [-inf/+inf]. To indicate no limit on *min* or *max* only, specify a hyphen (-). Normally, any NaNs encountered are simply skipped and not considered in the range-decision. Append **+n** to consider a NaN to be outside the given z-range. This means the new subset will be NaN-free. Alternatively, append **+r** to consider NaNs to be within the data range. In this case we stop shrinking the boundaries once a NaN is found [Default simply skips NaNs when making the range decision]. Finally, if your core subset grid is surrounded by rows and/or columns that are all NaNs, append **+N** to strip off such columns before (optionally) considering the range of the core subset for further reduction of the area. {V} Returns ------- ret: xarray.DataArray or None Return type depends on whether the ``outgrid`` parameter is set: - :class:`xarray.DataArray` if ``outgrid`` is not set - None if ``outgrid`` is set (grid output will be stored in file set by ``outgrid``) """ kind = data_kind(grid) with GMTTempFile(suffix=".nc") as tmpfile: with Session() as lib: if kind == "file": file_context = dummy_context(grid) elif kind == "grid": file_context = lib.virtualfile_from_grid(grid) else: raise GMTInvalidInput("Unrecognized data type: {}".format(type(grid))) with file_context as infile: if "G" not in kwargs.keys(): # if outgrid is unset, output to tempfile kwargs.update({"G": tmpfile.name}) outgrid = kwargs["G"] arg_str = " ".join([infile, build_arg_string(kwargs)]) lib.call_module("grdcut", arg_str) if outgrid == tmpfile.name: # if user did not set outgrid, return DataArray with xr.open_dataarray(outgrid) as dataarray: result = dataarray.load() _ = result.gmt # load GMTDataArray accessor information else: result = None # if user sets an outgrid, return None return result