"""
Function to download the EGM2008 Earth geoid 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_geoid"]
[docs]
def load_earth_geoid(
resolution: Literal[
"01d", "30m", "20m", "15m", "10m", "06m", "05m", "04m", "03m", "02m", "01m"
] = "01d",
region: Sequence[float] | str | None = None,
registration: Literal["gridline", "pixel"] = "gridline",
) -> xr.DataArray:
r"""
Load the EGM2008 Earth geoid dataset in various resolutions.
.. figure:: https://www.generic-mapping-tools.org/remote-datasets/_images/GMT_earth_geoid.jpg
:width: 80 %
:align: center
EGM2008 Earth geoid dataset.
This function downloads the dataset from the GMT data server, caches it in a user
data directory (usually ``~/.gmt/server/earth/earth_geoid/``), 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 dataset can also be accessed by specifying a file name in any grid processing
function or plotting method, using the following file name format:
**@earth_geoid**\_\ *res*\_\ *reg*. *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_geoid_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_geoid``),
GMT automatically selects a suitable resolution based on the current region and
projection settings.
Refer to :gmt-datasets:`earth-geoid.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.
Returns
-------
grid
The Earth geoid grid. Coordinates are latitude and
longitude in degrees. Units are in meters.
Note
----
The registration and coordinate system type of the returned
:class:`xarray.DataArray` grid can be accessed via the *gmt* accessor. Refer to
:class:`pygmt.GMTDataArrayAccessor` for detailed explanations and limitations.
Examples
--------
>>> from pygmt.datasets import load_earth_geoid
>>> # Load the default grid (gridline-registered 1 arc-degree grid)
>>> grid = load_earth_geoid()
>>> # Load the 30 arc-minutes grid with "gridline" registration
>>> grid = load_earth_geoid(resolution="30m", registration="gridline")
>>> # Load high-resolution (5 arc-minutes) grid for a specific region
>>> grid = load_earth_geoid(
... resolution="05m",
... region=[120, 160, 30, 60],
... registration="gridline",
... )
"""
grid = _load_remote_dataset(
name="earth_geoid",
prefix="earth_geoid",
resolution=resolution,
region=region,
registration=registration,
)
return grid