"""
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* setting 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:
- xarray.DataArray if *outgrid* is not set
- None if *outgrid* is set (grid output will be stored in *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