"""
Function to download the IGPP Earth free-air anomaly and uncertainty 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_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,
uncertainty: bool = False,
) -> xr.DataArray:
r"""
Load the IGPP Earth free-air anomaly and uncertainty datasets in various
resolutions.
.. list-table::
:widths: 50 50
:header-rows: 1
* - IGPP Earth free-air anomaly
- IGPP Earth free-air anomaly uncertainty
* - .. figure:: https://www.generic-mapping-tools.org/remote-datasets/_images/GMT_earth_faa.jpg
- .. figure:: https://www.generic-mapping-tools.org/remote-datasets/_images/GMT_earth_faaerror.jpg
The grids are downloaded to a user data directory (usually
``~/.gmt/server/earth/earth_faa/`` or ``~/.gmt/server/earth/earth_faaerror/``) the
first time you invoke this function. Afterwards, it will load the grid from 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_type**\_\ *res*\[_\ *reg*] to any grid processing function or
plotting method. *earth_faa_type* is the GMT name for the dataset. The available
options are **earth_faa** and **earth_faaerror**. *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 tables (CPTs) for these datasets are *@earth_faa.cpt* and
*@earth_faaerror.cpt*. The dataset-specific CPT is 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"`` or
``cmap="@earth_faaerror.cpt"``.
Refer to :gmt-datasets:`earth-faa.html` and :gmt-datasets:`earth-faaerror.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.
uncertainty
By default, the Earth free-air anomaly values are returned. Set to ``True`` to
return the related uncertainties instead.
Returns
-------
grid
The Earth free-air anomaly (uncertainty) grid. Coordinates are latitude and
longitude in degrees. Values and uncertainties 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 uncertainties related to the default grid
>>> grid = load_earth_free_air_anomaly(uncertainty=True)
>>> # 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"
... )
"""
prefix = "earth_faaerror" if uncertainty is True else "earth_faa"
grid = _load_remote_dataset(
name=prefix,
prefix=prefix,
resolution=resolution,
region=region,
registration=registration,
)
return grid