"""
Function to download the IGPP Earth free-air anomaly dataset 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_free_air_anomaly"]
[docs]
def load_earth_free_air_anomaly(
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,
) -> xr.DataArray:
r"""
Load the IGPP Earth free-air anomaly dataset in various resolutions.
.. figure:: https://www.generic-mapping-tools.org/remote-datasets/_images/GMT_earth_faa.jpg
:width: 80 %
:align: center
IGPP Earth free-air anomaly dataset.
The grids are downloaded to a user data directory
(usually ``~/.gmt/server/earth/earth_faa/``) the first time you invoke
this function. Afterwards, it will load the grid from the data directory.
So you'll need an internet connection the first time around.
These grids can also be accessed by passing in the file name
**@earth_faa**\_\ *res*\[_\ *reg*] to any grid processing function or
plotting method. *res* is the grid resolution (see below), and *reg* is
the grid registration type (**p** for pixel registration or **g** for
gridline registration).
The default color palette table (CPT) for this dataset is *@earth_faa.cpt*.
It's implicitly used when passing in the file name of the dataset to any
grid plotting method if no CPT is explicitly specified. When the dataset
is loaded and plotted as an :class:`xarray.DataArray` object, the default
CPT is ignored, and GMT's default CPT (*turbo*) is used. To use the
dataset-specific CPT, you need to explicitly set ``cmap="@earth_faa.cpt"``.
Refer to :gmt-datasets:`earth-faa.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``, means
``"gridline"`` for all resolutions except ``"01m"`` which is
``"pixel"`` only.
Returns
-------
grid
The Earth free-air anomaly grid. Coordinates are latitude and
longitude in degrees. Units are in mGal.
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_free_air_anomaly
>>> # load the default grid (gridline-registered 1 arc-degree grid)
>>> grid = load_earth_free_air_anomaly()
>>> # load the 30 arc-minutes grid with "gridline" registration
>>> grid = load_earth_free_air_anomaly(resolution="30m", registration="gridline")
>>> # load high-resolution (5 arc-minutes) grid for a specific region
>>> grid = load_earth_free_air_anomaly(
... resolution="05m",
... region=[120, 160, 30, 60],
... registration="gridline",
... )
"""
grid = _load_remote_dataset(
name="earth_faa",
prefix="earth_faa",
resolution=resolution,
region=region,
registration=registration,
)
return grid