Source code for pygmt.accessors

"""
GMT accessor for :class:`xarray.DataArray`.
"""
from pathlib import Path

import xarray as xr
from pygmt.exceptions import GMTInvalidInput
from pygmt.src.grdinfo import grdinfo


[docs]@xr.register_dataarray_accessor("gmt") class GMTDataArrayAccessor: """ GMT accessor for :class:`xarray.DataArray`. The accessor extends :class:`xarray.DataArray` to store GMT-specific properties about grids, which are important for PyGMT to correctly process and plot the grids. Notes ----- Due to the limitations of xarray accessors, the GMT accessors are created once per :class:`xarray.DataArray` instance. You may lose these GMT-specific properties when manipulating grids (e.g., arithmetic and slice operations) or when accessing a :class:`xarray.DataArray` from a :class:`xarray.Dataset`. In these cases, you need to manually set these properties before passing the grid to PyGMT. Examples -------- For GMT's built-in remote datasets, these GMT-specific properties are automatically determined and you can access them as follows: >>> from pygmt.datasets import load_earth_relief >>> # Use the global Earth relief grid with 1 degree spacing >>> grid = load_earth_relief(resolution="01d", registration="pixel") >>> # See if grid uses Gridline (0) or Pixel (1) registration >>> grid.gmt.registration 1 >>> # See if grid uses Cartesian (0) or Geographic (1) coordinate system >>> grid.gmt.gtype 1 For :class:`xarray.DataArray` grids created by yourself, grid properties ``registration`` and ``gtype`` default to 0 (i.e., a gridline-registered, Cartesian grid). You need to set the correct properties before passing it to PyGMT functions: >>> import numpy as np >>> import pygmt >>> import xarray as xr >>> # create a DataArray in gridline coordinates of sin(lon) * cos(lat) >>> interval = 2.5 >>> lat = np.arange(90, -90 - interval, -interval) >>> lon = np.arange(0, 360 + interval, interval) >>> longrid, latgrid = np.meshgrid(lon, lat) >>> data = np.sin(np.deg2rad(longrid)) * np.cos(np.deg2rad(latgrid)) >>> grid = xr.DataArray( ... data, coords=[("latitude", lat), ("longitude", lon)] ... ) >>> # default to a gridline-registrated Cartesian grid >>> grid.gmt.registration, grid.gmt.gtype (0, 0) >>> # set it to a gridline-registered geographic grid >>> grid.gmt.registration = 0 >>> grid.gmt.gtype = 1 >>> grid.gmt.registration, grid.gmt.gtype (0, 1) Note that the accessors are created once per :class:`xarray.DataArray` instance, so you may lose these GMT-specific properties after manipulating your grid. Inplace assignment operators like ``*=`` don't create new instances, so the properties are still kept: >>> grid *= 2.0 >>> grid.gmt.registration, grid.gmt.gtype (0, 1) Other grid operations (e.g., arithmetic or slice operations) create new instances, so the properties will be lost: >>> # grid2 is a slice of the original grid >>> grid2 = grid[0:30, 50:80] >>> # properties are reset to the default values for new instance >>> grid2.gmt.registration, grid2.gmt.gtype (0, 0) >>> # need to set these properties before passing the grid to PyGMT >>> grid2.gmt.registration = grid.gmt.registration >>> grid2.gmt.gtype = grid.gmt.gtype >>> grid2.gmt.registration, grid2.gmt.gtype (0, 1) Accesing a :class:`xarray.DataArray` from a :class:`xarray.Dataset` always creates new instances, so these properties are always lost. The workaround is to assign the :class:`xarray.DataArray` into a variable: >>> ds = xr.Dataset({"zval": grid}) >>> ds.zval.gmt.registration, ds.zval.gmt.gtype (0, 0) >>> # manually set these properties won't work as expected >>> ds.zval.gmt.registration, ds.zval.gmt.gtype = 0, 1 >>> ds.zval.gmt.registration, ds.zval.gmt.gtype (0, 0) >>> # workaround: assign the DataArray into a variable >>> zval = ds.zval >>> zval.gmt.registration, zval.gmt.gtype (0, 0) >>> zval.gmt.registration, zval.gmt.gtype = 0, 1 >>> zval.gmt.registration, zval.gmt.gtype (0, 1) """ def __init__(self, xarray_obj): self._obj = xarray_obj self._source = self._obj.encoding.get("source") if self._source is not None and Path(self._source).exists(): try: # Get grid registration and grid type from the last two columns # of the shortened summary information of `grdinfo`. self._registration, self._gtype = map( int, grdinfo(self._source, per_column="n").split()[-2:] ) except ValueError: self._registration = 0 # Default to Gridline registration self._gtype = 0 # Default to Cartesian grid type else: self._registration = 0 # Default to Gridline registration self._gtype = 0 # Default to Cartesian grid type del self._source @property def registration(self): """ Registration type of the grid, either 0 (Gridline) or 1 (Pixel). """ return self._registration @registration.setter def registration(self, value): if value not in (0, 1): raise GMTInvalidInput( f"Invalid grid registration value: {value}, should be either " "0 for Gridline registration or 1 for Pixel registration." ) self._registration = value @property def gtype(self): """ Coordinate system type of the grid, either 0 (Cartesian) or 1 (Geographic). """ return self._gtype @gtype.setter def gtype(self, value): if value not in (0, 1): raise GMTInvalidInput( f"Invalid coordinate system type: {value}, should be " "either 0 for Cartesian or 1 for Geographic." ) self._gtype = value