"""
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 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_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