"""
grdtrack - Sample grids at specified (x,y) locations.
"""
import pandas as pd
from pygmt.clib import Session
from pygmt.exceptions import GMTInvalidInput
from pygmt.helpers import (
GMTTempFile,
build_arg_string,
data_kind,
dummy_context,
fmt_docstring,
use_alias,
)
[docs]@fmt_docstring
@use_alias(n="interpolation", V="verbose")
def grdtrack(points, grid, newcolname=None, outfile=None, **kwargs):
"""
Sample grids at specified (x,y) locations.
Grdtrack reads one or more grid files and a table with (x,y) [or (lon,lat)]
positions in the first two columns (more columns may be present). It
interpolates the grid(s) at the positions in the table and writes out the
table with the interpolated values added as (one or more) new columns. A
bicubic [Default], bilinear, B-spline or nearest-neighbor interpolation is
used, requiring boundary conditions at the limits of the region (see
``interpolation``; Default uses “natural” conditions (second partial
derivative normal to edge is zero) unless the grid is automatically
recognized as periodic.)
Full option list at :gmt-docs:`grdtrack.html`
{aliases}
Parameters
----------
points : pandas.DataFrame or str
Either a table with (x, y) or (lon, lat) values in the first two
columns, or a filename (e.g. csv, txt format). More columns may be
present.
grid : xarray.DataArray or str
Gridded array from which to sample values from, or a filename (netcdf
format).
newcolname : str
Required if ``points`` is a :class:`pandas.DataFrame`. The name for the
new column in the track :class:`pandas.DataFrame` table where the
sampled values will be placed.
outfile : str
Required if ``points`` is a file. The file name for the output ASCII
file.
{V}
{n}
Returns
-------
track: pandas.DataFrame or None
Return type depends on whether the ``outfile`` parameter is set:
- :class:`pandas.DataFrame` table with (x, y, ..., newcolname) if
``outfile`` is not set
- None if ``outfile`` is set (track output will be stored in file set
by ``outfile``)
"""
with GMTTempFile(suffix=".csv") as tmpfile:
with Session() as lib:
# Store the pandas.DataFrame points table in virtualfile
if data_kind(points) == "matrix":
if newcolname is None:
raise GMTInvalidInput("Please pass in a str to 'newcolname'")
table_context = lib.virtualfile_from_matrix(points.values)
elif data_kind(points) == "file":
if outfile is None:
raise GMTInvalidInput("Please pass in a str to 'outfile'")
table_context = dummy_context(points)
else:
raise GMTInvalidInput(f"Unrecognized data type {type(points)}")
# Store the xarray.DataArray grid in virtualfile
if data_kind(grid) == "grid":
grid_context = lib.virtualfile_from_grid(grid)
elif data_kind(grid) == "file":
grid_context = dummy_context(grid)
else:
raise GMTInvalidInput(f"Unrecognized data type {type(grid)}")
# Run grdtrack on the temporary (csv) points table
# and (netcdf) grid virtualfile
with table_context as csvfile:
with grid_context as grdfile:
kwargs.update({"G": grdfile})
if outfile is None: # Output to tmpfile if outfile is not set
outfile = tmpfile.name
arg_str = " ".join(
[csvfile, build_arg_string(kwargs), "->" + outfile]
)
lib.call_module(module="grdtrack", args=arg_str)
# Read temporary csv output to a pandas table
if outfile == tmpfile.name: # if user did not set outfile, return pd.DataFrame
column_names = points.columns.to_list() + [newcolname]
result = pd.read_csv(tmpfile.name, sep="\t", names=column_names)
elif outfile != tmpfile.name: # return None if outfile set, output in outfile
result = None
return result