"""
Function to download the Mercury relief 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_mercury_relief"]
[docs]
def load_mercury_relief(
resolution: Literal[
"01d",
"30m",
"20m",
"15m",
"10m",
"06m",
"05m",
"04m",
"03m",
"02m",
"01m",
"56s",
] = "01d",
region: Sequence[float] | str | None = None,
registration: Literal["gridline", "pixel", None] = None,
) -> xr.DataArray:
r"""
Load the Mercury relief dataset in various resolutions.
.. figure:: https://www.generic-mapping-tools.org/remote-datasets/_images/GMT_mercury_relief.jpg
:width: 80%
:align: center
Mercury relief dataset.
This function downloads the dataset from the GMT data server, caches it in a user
data directory (usually ``~/.gmt/server/mercury/mercury_relief/``), 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:
**@mercury_relief**\_\ *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., ``@mercury_relief_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., ``@mercury_relief``), GMT automatically selects a suitable resolution
based on the current region and projection settings.
This dataset comes with a color palette table (CPT) file, ``@mercury_relief.cpt``.
To use the dataset-specific CPT when plotting the dataset, explicitly set
``cmap="@mercury_relief.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:`mercury-relief.html` for more details about available
datasets, including version information and references.
Parameters
----------
resolution
The grid resolution. The suffix ``d``, ``m`` and ``s`` stand for arc-degrees,
arc-minutes and arc-seconds. Note that ``"56s"`` refers to a resolution of
56.25 arc-seconds.
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 for ``"56s"`` which is ``"pixel"``
only.
Returns
-------
grid
The Mercury relief grid. Coordinates are latitude and longitude in degrees.
Relief is 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_mercury_relief
>>> # Load the default grid (gridline-registered 1 arc-degree grid)
>>> grid = load_mercury_relief()
>>> # Load the 30 arc-minutes grid with "gridline" registration
>>> grid = load_mercury_relief(resolution="30m", registration="gridline")
>>> # Load high-resolution (5 arc-minutes) grid for a specific region
>>> grid = load_mercury_relief(
... resolution="05m",
... region=[120, 160, 30, 60],
... registration="gridline",
... )
"""
grid = _load_remote_dataset(
name="mercury_relief",
prefix="mercury_relief",
resolution=resolution,
region=region,
registration=registration,
)
return grid