"""
Function to download the IGPP Earth east-west and north-south deflection datasets from
the GMT data server, and load as :class:`xarray.DataArray`.
The grids are available in various resolutions.
"""
from collections.abc import Sequence
from typing import Literal
import xarray as xr
from pygmt.datasets.load_remote_dataset import _load_remote_dataset
__doctest_skip__ = ["load_earth_deflection"]
[docs]
def load_earth_deflection(
resolution: Literal[
"01d", "30m", "20m", "15m", "10m", "06m", "05m", "04m", "03m", "02m", "01m"
] = "01d",
region: Sequence[float] | str | None = None,
registration: Literal["gridline", "pixel", None] = None,
component: Literal["east", "north"] = "east",
) -> xr.DataArray:
r"""
Load the IGPP Earth east-west and north-south deflection datasets in various
resolutions.
.. list-table::
:widths: 50 50
:header-rows: 1
* - IGPP Earth east-west deflection
- IGPP Earth north-south deflection
* - .. figure:: https://www.generic-mapping-tools.org/remote-datasets/_images/GMT_earth_edefl.jpg
- .. figure:: https://www.generic-mapping-tools.org/remote-datasets/_images/GMT_earth_ndefl.jpg
This function downloads the dataset from the GMT data server, caches it in a user
data directory (usually ``~/.gmt/server/earth/earth_edefl/`` and
``~/.gmt/server/earth/earth_ndefl/``), and load the dataset as an
:class:`xarray.DataArray`. An internet connection is required the first time around,
but subsequent calls will load the dataset from the local data directory.
The datasets can also be accessed by specifying a file name in any grid processing
function or plotting method, using the following file name format:
**@**\ *earth_defl_type*\_\ *res*\_\ *reg*. *earth_defl_type* is the GMT name for
the dataset. The available options are **earth_edefl** and **earth_ndefl**; *res* is
the grid resolution; *reg* is the grid registration type (**p** for pixel
registration, **g** for gridline registration). If *reg* is omitted (e.g.,
``@earth_edefl_01d``), the gridline-registered grid will be loaded for grid
processing functions and the pixel-registered grid will be loaded for plotting
functions. If *res* is also omitted (i.e., ``@earth_edefl``), GMT automatically
selects a suitable resolution based on the current region and projection settings.
This dataset comes with a color palette table (CPT) file, ``@earth_defl.cpt``. To
use the dataset-specific CPT when plotting the dataset, explicitly set
``cmap="@earth_defl.cpt"``, otherwise GMT's default CPT (*turbo*) will be used. If
the dataset is referenced by the file name in a grid plotting method, the
dataset-specific CPT file is used automatically unless another CPT is specified.
Refer to :gmt-datasets:`earth-edefl.html` and :gmt-datasets:`earth-ndefl.html` for
more details about available datasets, including version information and references.
Parameters
----------
resolution
The grid resolution. The suffix ``d`` and ``m`` stand for arc-degrees and
arc-minutes.
region
The subregion of the grid to load, in the form of a sequence [*xmin*, *xmax*,
*ymin*, *ymax*] or an ISO country code. Required for grids with resolutions
higher than 5 arc-minutes (i.e., ``"05m"``).
registration
Grid registration type. Either ``"pixel"`` for pixel registration or
``"gridline"`` for gridline registration. Default is ``None``, which means
``"gridline"`` for all resolutions except ``"01m"`` which is ``"pixel"`` only.
component
By default, the east-west deflection (``component="east"``) is returned,
set ``component="north"`` to return the north-south deflection.
Returns
-------
grid
The Earth east-west or north-south deflection grid. Coordinates are latitude
and longitude in degrees. Deflection values are in micro-radians, where
positive (negative) values indicate a deflection to the east or north (west
or south).
Note
----
The registration and coordinate system type of the returned
:class:`xarray.DataArray` grid can be accessed via the GMT accessors (i.e.,
``grid.gmt.registration`` and ``grid.gmt.gtype`` respectively). However, these
properties may be lost after specific grid operations (such as slicing) and will
need to be manually set before passing the grid to any PyGMT data processing or
plotting functions. Refer to :class:`pygmt.GMTDataArrayAccessor` for detailed
explanations and workarounds.
Examples
--------
>>> from pygmt.datasets import load_earth_deflection
>>> # Load the default grid for east-west deflection (gridline-registered
>>> # 1 arc-degree grid)
>>> grid = load_earth_deflection()
>>> # Load the default grid for north-south deflection
>>> grid = load_earth_deflection(component="north")
>>> # Load the 30 arc-minutes grid with "gridline" registration
>>> grid = load_earth_deflection(resolution="30m", registration="gridline")
>>> # Load high-resolution (5 arc-minutes) grid for a specific region
>>> grid = load_earth_deflection(
... resolution="05m", region=[120, 160, 30, 60], registration="gridline"
... )
"""
prefix = "earth_ndefl" if component == "north" else "earth_edefl"
grid = _load_remote_dataset(
name=prefix,
prefix=prefix,
resolution=resolution,
region=region,
registration=registration,
)
return grid