"""
Function to download the GSHHG Earth distance to shoreline 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_dist"]
[docs]
def load_earth_dist(
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 GSHHG Earth distance to shoreline dataset in various resolutions.
.. figure:: https://www.generic-mapping-tools.org/remote-datasets/_images/GMT_earth_dist.jpg
:width: 80 %
:align: center
GSHHG Earth distance to shoreline dataset.
The grids are downloaded to a user data directory (usually
``~/.gmt/server/earth/earth_dist/``) 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_dist**\_\ *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_dist.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_dist.cpt"``.
Refer to :gmt-datasets:`earth-dist.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 GSHHG Earth distance to shoreline grid. Coordinates are latitude and
longitude in degrees. Distances are in kilometers, where positive (negative)
values mean land to coastline (ocean to coastline).
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_dist
>>> # load the default grid (gridline-registered 1 arc-degree grid)
>>> grid = load_earth_dist()
>>> # load the 30 arc-minutes grid with "gridline" registration
>>> grid = load_earth_dist(resolution="30m", registration="gridline")
>>> # load high-resolution (5 arc-minutes) grid for a specific region
>>> grid = load_earth_dist(
... resolution="05m",
... region=[120, 160, 30, 60],
... registration="gridline",
... )
"""
grid = _load_remote_dataset(
name="earth_dist",
prefix="earth_dist",
resolution=resolution,
region=region,
registration=registration,
)
return grid