"""
Function to download the Earth relief 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
from pygmt.exceptions import GMTInvalidInput
__doctest_skip__ = ["load_earth_relief"]
[docs]
def load_earth_relief(
resolution: Literal[
"01d",
"30m",
"20m",
"15m",
"10m",
"06m",
"05m",
"04m",
"03m",
"02m",
"01m",
"30s",
"15s",
"03s",
"01s",
] = "01d",
region: Sequence[float] | str | None = None,
registration: Literal["gridline", "pixel", None] = None,
data_source: Literal["igpp", "gebco", "gebcosi", "synbath"] = "igpp",
use_srtm: bool = False,
) -> xr.DataArray:
r"""
Load the Earth relief datasets (topography and bathymetry) in various resolutions.
.. figure:: https://www.generic-mapping-tools.org/remote-datasets/_images/GMT_earth_gebco.jpg
:width: 80 %
:align: center
Earth relief datasets (topography and bathymetry).
The grids are downloaded to a user data directory
(usually ``~/.gmt/server/earth/earth_relief``,
``~/.gmt/server/earth/earth_gebco``, ``~/.gmt/server/earth/earth_gebcosi``,
or ``~/.gmt/server/earth/earth_synbath``) 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.
This module downloads the grids that can also be accessed by
passing in the file name **@**\ *earth_relief_type*\_\ *res*\[_\ *reg*] to
any grid processing function or plotting method. *earth_relief_type* is
the GMT name for the dataset. The available options are **earth_relief**\,
**earth_gebco**\, **earth_gebcosi**\, and **earth_synbath**\. *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 *geo*.
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="geo"``.
Refer to :gmt-datasets:`earth-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.
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``, means
``"gridline"`` for all resolutions except ``"15s"`` which is
``"pixel"`` only.
data_source
Select the source for the Earth relief data. Available options are:
- ``"igpp"``: IGPP Earth Relief. See
:gmt-datasets:`earth-relief.html`.
- ``"synbath"``: IGPP Earth Relief dataset that uses stastical
properties of young seafloor to provide a more realistic relief
of young areas with small seamounts.
- ``"gebco"``: GEBCO Earth Relief with only observed relief and
inferred relief via altimetric gravity. See
:gmt-datasets:`earth-gebco.html`.
- ``"gebcosi"``: GEBCO Earth Relief that gives sub-ice (si) elevations.
use_srtm
By default, the land-only SRTM tiles from NASA are used to generate the
``"03s"`` and ``"01s"`` grids, and the missing ocean values are filled
by up-sampling the SRTM15 tiles which have a resolution of 15
arc-seconds (i.e., ``"15s"``). If True, will only load the original
land-only SRTM tiles. Only works when ``data_source="igpp"``.
Returns
-------
grid
The Earth 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_earth_relief
>>> # load the default grid (gridline-registered 1 arc-degree grid)
>>> grid = load_earth_relief()
>>> # load the 30 arc-minutes grid with "gridline" registration
>>> grid = load_earth_relief(resolution="30m", registration="gridline")
>>> # load high-resolution (5 arc-minutes) grid for a specific region
>>> grid = load_earth_relief(
... resolution="05m",
... region=[120, 160, 30, 60],
... registration="gridline",
... )
>>> # load the original 3 arc-seconds land-only SRTM tiles from NASA
>>> grid = load_earth_relief(
... resolution="03s",
... region=[135, 136, 35, 36],
... registration="gridline",
... use_srtm=True,
... )
"""
# resolutions of original land-only SRTM tiles from NASA
land_only_srtm_resolutions = ["03s", "01s"]
# Map data source to prefix
prefix = {
"igpp": "earth_relief",
"gebco": "earth_gebco",
"gebcosi": "earth_gebcosi",
"synbath": "earth_synbath",
}.get(data_source)
if prefix is None:
raise GMTInvalidInput(
f"Invalid earth relief data source '{data_source}'. "
"Valid values are 'igpp', 'gebco', 'gebcosi', and 'synbath'."
)
# Use SRTM or not.
if use_srtm and resolution in land_only_srtm_resolutions:
if data_source != "igpp":
raise GMTInvalidInput(
f"Option 'use_srtm=True' doesn't work with data source '{data_source}'."
" Please set 'data_source' to 'igpp'."
)
prefix = "srtm_relief"
# Choose earth relief dataset
match data_source:
case "igpp" | "synbath":
name = "earth_igpp"
case "gebco" | "gebcosi":
name = "earth_gebco"
grid = _load_remote_dataset(
name=name,
prefix=prefix,
resolution=resolution,
region=region,
registration=registration,
)
return grid