Add Mars dataset

pygmt/datasets/__init__.py

@@ -6,6 +6,7 @@
 from pygmt.datasets.samples import (
     load_fractures_compilation,
     load_japan_quakes,
+    load_mars_shape,
     load_ocean_ridge_points,
     load_sample_bathymetry,
     load_usgs_quakes,

pygmt/datasets/samples.py

@@ -123,3 +123,27 @@ def load_fractures_compilation():
     fname = which("@fractures_06.txt", download="c")
     data = pd.read_csv(fname, header=None, sep=r"\s+", names=["azimuth", "length"])
     return data[["length", "azimuth"]]
+
+
+def load_mars_shape():
+    """
+    Load a table of data for the shape of Mars.
+
+    This is the ``@mars370d.txt`` dataset used in GMT examples, with data and
+    information from Smith, D. E., and M. T. Zuber (1996), The shape of Mars
+    and the topographic signature of the hemispheric dichotomy. Data columns
+    are "longitude," "latitude", and "radius (meters)."
+
+    The data are downloaded to a cache directory (usually ``~/.gmt/cache``) the
+    first time you invoke this function. Afterwards, it will load the data from
+    the cache. So you'll need an internet connection the first time around.
+
+    Returns
+    -------
+    data : pandas.DataFrame
+        The data table. Use ``print(data.describe())`` to see the available
+        columns.
+    """
+    fname = which("@mars370d.txt", download="c")
+    data = pd.read_csv(fname, sep="\t", header=None, names=["lon", "lat", "radius(m)"])
+    return data

pygmt/tests/test_datasets_samples.py

@@ -4,6 +4,7 @@
 from pygmt.datasets import (
     load_fractures_compilation,
     load_japan_quakes,
+    load_mars_shape,
     load_ocean_ridge_points,
     load_sample_bathymetry,
     load_usgs_quakes,
@@ -72,3 +73,18 @@ def test_fractures_compilation():
     assert summary.loc["max", "length"] == 984.652
     assert summary.loc["min", "azimuth"] == 0.0
     assert summary.loc["max", "azimuth"] == 360.0
+
+
+def test_mars_shape():
+    """
+    Check that the @mars370d.txt dataset loads without errors.
+    """
+    data = load_mars_shape()
+    assert data.shape == (370, 3)
+    summary = data.describe()
+    assert summary.loc["min", "lon"] == 0.008
+    assert summary.loc["max", "lon"] == 359.983
+    assert summary.loc["min", "lat"] == -79.715
+    assert summary.loc["max", "lat"] == 85.887
+    assert summary.loc["min", "radius(m)"] == -6930
+    assert summary.loc["max", "radius(m)"] == 15001