Add load_earth_mask function for GSHHG Global Earth Mask dataset

[willschlitzer]

Add load_earth_mask to load the remote GSHHG Global Earth Mask dataset.

Addresses: #1786

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[willschlitzer]

/format

[seisman]

This function now returns a dataarray like below:

<xarray.DataArray 'z' (lat: 181, lon: 361)>
array([[1., 1., 1., ..., 1., 1., 1.],
       [1., 1., 1., ..., 1., 1., 1.],
       [1., 1., 1., ..., 1., 1., 1.],
       ...,
       [0., 0., 0., ..., 0., 0., 0.],
       [0., 0., 0., ..., 0., 0., 0.],
       [0., 0., 0., ..., 0., 0., 0.]], dtype=float32)
Coordinates:
  * lon      (lon) float64 -180.0 -179.0 -178.0 -177.0 ... 178.0 179.0 180.0
  * lat      (lat) float64 -90.0 -89.0 -88.0 -87.0 -86.0 ... 87.0 88.0 89.0 90.0
Attributes:
    long_name:     z
    actual_range:  [0. 2.]

The data dtype is float32, but the original grid @earth_mask_01d_g contains int8 values. Ideally, the function should return a grid with integer values.

[willschlitzer]

How would I change the value types across the entire array?

[seisman]

How would I change the value types across the entire array?

I don't know. Need to read the xarray docs.

[seisman]

Likely we need to use xarray.DataArray.astype to convert the data from float32 to int8, i.e., return grid.astype("int8").

[willschlitzer]

It looks like the number of if statements in _load_remote_dataset() is causing a style check failure. Should I refactor _load_remote_dataset() to use some smaller functions (i.e. _get_registration and _get_resolution) or use pylint: disable=too-many-branches?

[seisman]

use pylint: disable=too-many-branches?

This sounds good to me.