Fix #110: Ensure spectrogram plotting correctly handles non-UTC time scales

changelog/144.bugfix.rst

@@ -0,0 +1 @@
+Fixed an issue where plotting spectrograms with non-UTC time scales (e.g., 'tt') would result in time offsets by ensuring conversion to UTC before plotting.

pytest.ini

@@ -41,3 +41,5 @@ filterwarnings =
     ignore:The --rsyncdir command line argument and rsyncdirs config variable are deprecated.:DeprecationWarning
     ignore:File may have been truncated.*
     ignore:pattern has been replaced with the format keyword
+    # pyparsing deprecation warning from old matplotlib in oldestdeps
+    ignore:.*deprecated:pyparsing.warnings.PyparsingDeprecationWarning

radiospectra/mixins.py

@@ -18,9 +18,10 @@ def plot(self, axes=None, **kwargs):
         -------
         `matplotlib.collections.QuadMesh`
         """
-        import matplotlib.dates as mdates
         from matplotlib import pyplot as plt
 
+        from astropy.visualization import time_support
+
         if axes is None:
             fig, axes = plt.subplots()
         else:
@@ -36,17 +37,15 @@ def plot(self, axes=None, **kwargs):
             title = f"{title}, {self.detector}"
 
         axes.set_title(title)
-        axes.plot(self.times.datetime[[0, -1]], self.frequencies[[0, -1]], linestyle="None", marker="None")
-        if self.times.shape[0] == self.data.shape[0] and self.frequencies.shape[0] == self.data.shape[1]:
-            ret = axes.pcolormesh(self.times.datetime, self.frequencies.value, data, shading="auto", **kwargs)
-        else:
-            ret = axes.pcolormesh(self.times.datetime, self.frequencies.value, data[:-1, :-1], shading="auto", **kwargs)
-        axes.set_xlim(self.times.datetime[0], self.times.datetime[-1])
-        locator = mdates.AutoDateLocator(minticks=4, maxticks=8)
-        formatter = mdates.ConciseDateFormatter(locator)
-        axes.xaxis.set_major_locator(locator)
-        axes.xaxis.set_major_formatter(formatter)
-        fig.autofmt_xdate()
+        with time_support():
+            axes.plot(self.times[[0, -1]], self.frequencies[[0, -1]], linestyle="None", marker="None")
+            if self.times.shape[0] == self.data.shape[0] and self.frequencies.shape[0] == self.data.shape[1]:
+                ret = axes.pcolormesh(self.times, self.frequencies.value, data, shading="auto", **kwargs)
+            else:
+                ret = axes.pcolormesh(self.times, self.frequencies.value, data[:-1, :-1], shading="auto", **kwargs)
+            axes.set_xlim(self.times[0], self.times[-1])
+            fig.autofmt_xdate()
+
         # Set current axes/image if pyplot is being used (makes colorbar work)
         for i in plt.get_fignums():
             if axes in plt.figure(i).axes:
@@ -61,13 +60,18 @@ class NonUniformImagePlotMixin:
     """
 
     def plotim(self, fig=None, axes=None, **kwargs):
-        import matplotlib.dates as mdates
         from matplotlib import pyplot as plt
         from matplotlib.image import NonUniformImage
 
+        from astropy.visualization import time_support
+
         if axes is None:
             fig, axes = plt.subplots()
 
-        im = NonUniformImage(axes, interpolation="none", **kwargs)
-        im.set_data(mdates.date2num(self.times.datetime), self.frequencies.value, self.data)
-        axes.images.append(im)
+        with time_support():
+            axes.plot(self.times[[0, -1]], self.frequencies[[0, -1]], linestyle="None", marker="None")
+            im = NonUniformImage(axes, interpolation="none", **kwargs)
+            im.set_data(axes.convert_xunits(self.times), self.frequencies.value, self.data)
+            axes.add_image(im)
+            axes.set_xlim(self.times[0], self.times[-1])
+            axes.set_ylim(self.frequencies.value[0], self.frequencies.value[-1])

radiospectra/spectrogram/tests/conftest.py

@@ -0,0 +1,3 @@
+import matplotlib
+
+matplotlib.use("Agg")

radiospectra/spectrogram/tests/test_spectrogrambase.py

@@ -0,0 +1,57 @@
+from unittest import mock
+
+import matplotlib.pyplot as plt
+import numpy as np
+
+import astropy.units as u
+from astropy.time import Time
+
+from radiospectra.spectrogram.spectrogrambase import GenericSpectrogram
+
+
+def _get_spectrogram_with_time_scale(scale):
+    times = Time("2020-01-01T00:00:00", format="isot", scale=scale) + np.arange(4) * u.min
+    frequencies = np.linspace(10, 40, 4) * u.MHz
+    meta = {
+        "observatory": "Test",
+        "instrument": "TestInst",
+        "detector": "TestDet",
+        "start_time": times[0],
+        "end_time": times[-1],
+        "wavelength": np.array([1, 10]) * u.m,
+        "times": times,
+        "freqs": frequencies,
+    }
+    return GenericSpectrogram(np.arange(16).reshape(4, 4), meta)
+
+
+def test_plot_uses_time_support_for_datetime_conversion():
+    spec = _get_spectrogram_with_time_scale("tt")
+
+    mesh = spec.plot()
+    x_limits = np.array(mesh.axes.get_xlim())
+    expected_tt_limits = mesh.axes.convert_xunits(spec.times[[0, -1]])
+
+    plt.close(mesh.axes.figure)
+
+    np.testing.assert_allclose(x_limits, expected_tt_limits)
+
+
+def test_plotim_uses_time_support_for_datetime_conversion():
+    spec = _get_spectrogram_with_time_scale("tt")
+    fig, axes = plt.subplots()
+
+    with (
+        mock.patch("matplotlib.image.NonUniformImage.set_interpolation", autospec=True),
+        mock.patch("matplotlib.image.NonUniformImage.set_data", autospec=True) as set_data,
+    ):
+        spec.plotim(fig=fig, axes=axes)
+
+    plt.close(fig)
+
+    _, x_values, y_values, image = set_data.call_args.args
+    expected_tt = axes.convert_xunits(spec.times)
+
+    np.testing.assert_allclose(x_values, expected_tt)
+    np.testing.assert_allclose(y_values, spec.frequencies.value)
+    np.testing.assert_allclose(image, spec.data)