pygmt.datasets.load_earth_free_air_anomaly

pygmt.datasets.load_earth_free_air_anomaly(resolution='01d', region=None, registration=None, uncertainty=False)[source]

Load the IGPP Earth free-air anomaly and uncertainty datasets in various resolutions.

IGPP Earth free-air anomaly

IGPP Earth free-air anomaly uncertainty
https://www.generic-mapping-tools.org/remote-datasets/_images/GMT_earth_faa.jpg
https://www.generic-mapping-tools.org/remote-datasets/_images/GMT_earth_faaerror.jpg

The grids are downloaded to a user data directory (usually ~/.gmt/server/earth/earth_faa/ or ~/.gmt/server/earth/earth_faaerror/) the first time you invoke this function. Afterwards, it will load the grid from 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_faa_type_res[_reg] to any grid processing function or plotting method. earth_faa_type is the GMT name for the dataset. The available options are earth_faa and earth_faaerror. 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 tables (CPTs) for these datasets are @earth_faa.cpt and @earth_faaerror.cpt. The dataset-specific CPT is 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 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_faa.cpt" or cmap="@earth_faaerror.cpt".

Refer to https://www.generic-mapping-tools.org/remote-datasets/earth-faa.html and https://www.generic-mapping-tools.org/remote-datasets/earth-faaerror.html for more details about available datasets, including version information and references.

Parameters:

  • resolution (Literal['01d', '30m', '20m', '15m', '10m', '06m', '05m', '04m', '03m', '02m', '01m'], default: '01d') – The grid resolution. The suffix d and m stand for arc-degrees and arc-minutes.

  • region (Sequence[float] | str | None, default: None) – 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 (Literal['gridline', 'pixel', None], default: None) – Grid registration type. Either "pixel" for pixel registration or "gridline" for gridline registration. Default is None, which means "gridline" for all resolutions except "01m" which is "pixel" only.

  • uncertainty (bool, default: False) – By default, the Earth free-air anomaly values are returned. Set to True to return the related uncertainties instead.

Return type:

DataArray

Returns:

grid – The Earth free-air anomaly (uncertainty) grid. Coordinates are latitude and longitude in degrees. Values and uncertainties are in mGal.

Note

The registration and coordinate system type of the returned 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 pygmt.GMTDataArrayAccessor for detailed explanations and workarounds.

Examples

>>> from pygmt.datasets import load_earth_free_air_anomaly
>>> # load the default grid (gridline-registered 1 arc-degree grid)
>>> grid = load_earth_free_air_anomaly()
>>> # load the uncertainties related to the default grid
>>> grid = load_earth_free_air_anomaly(uncertainty=True)
>>> # load the 30 arc-minutes grid with "gridline" registration
>>> grid = load_earth_free_air_anomaly(resolution="30m", registration="gridline")
>>> # load high-resolution (5 arc-minutes) grid for a specific region
>>> grid = load_earth_free_air_anomaly(
...     resolution="05m", region=[120, 160, 30, 60], registration="gridline"
... )