use correct spectral density equivalencies for marker unit changes (s…

…pacetelescope#3219)

* get spectral density equivalencies from original quantities

* add change log

* remove using spectrum1d object

* add test coverage to ensure marker location updates with uc

* use input data instead of slice plugin for truth in tests

CHANGES.rst

@@ -6,7 +6,7 @@ New Features
 
 - Added flux/surface brightness translation and surface brightness
   unit conversion in Cubeviz and Specviz. [#2781, #2940, #3088, #3111, #3113, #3129,
-  #3139, #3149, #3155, #3178, #3185, #3187, #3190, #3156, #3200, #3192, #3206, #3211, #3216]
+  #3139, #3149, #3155, #3178, #3185, #3187, #3190, #3156, #3200, #3192, #3206, #3211, #3216, #3219]
 
 - Plugin tray is now open by default. [#2892]
 

jdaviz/configs/default/plugins/markers/tests/test_markers_plugin.py

@@ -117,6 +117,28 @@ def test_markers_cubeviz(tmp_path, cubeviz_helper, spectrum1d_cube):
 
     mp._obj._on_viewer_key_event(sv, {'event': 'keydown',
                                       'key': 'm'})
+
+    # test that markers update on unit conversion
+    uc = cubeviz_helper.plugins['Unit Conversion']
+    uc.flux_unit.selected = 'MJy'
+
+    # find the index of the marker's x-coordinate in the spectral axis of the original input data
+    spec = cubeviz_helper.get_data('Spectrum (sum)', use_display_units=True)
+    marker_index = np.where(spec.spectral_axis.value == mp._obj.marks['cubeviz-2'].x)
+    # use the index to find the associated flux value of the original input
+    flux_value = spec.flux[marker_index].value
+
+    # compare the marker's (y) flux value with the flux value of the original input data
+    assert_allclose(mp._obj.marks['cubeviz-2'].y[0], flux_value)
+
+    # now check if marks update with a unit that requires spectral density equivalency
+    uc.flux_unit.selected = 'erg / (Angstrom s cm2)'
+
+    spec = cubeviz_helper.get_data('Spectrum (sum)', use_display_units=True)
+    flux_value = spec.flux[marker_index].value
+
+    assert_allclose(mp._obj.marks['cubeviz-2'].y[0], flux_value)
+
     assert len(mp.export_table()) == 3
     assert len(_get_markers_from_viewer(fv).x) == 1
     assert len(_get_markers_from_viewer(sv).x) == 2

jdaviz/core/marks.py

@@ -127,8 +127,10 @@ def set_y_unit(self, unit=None):
 
         if self.yunit is not None and not np.all([s == 0 for s in self.y.shape]):
             if self.viewer.default_class is Spectrum1D:
+                # used to obtain spectral density equivalencies with previous data and units
+                eqv = u.spectral_density(self.x*self.xunit)
+
                 spec = self.viewer.state.reference_data.get_object(cls=Spectrum1D)
-                eqv = u.spectral_density(spec.spectral_axis)
 
                 if ('_pixel_scale_factor' in spec.meta):
                     eqv += _eqv_pixar_sr(spec.meta['_pixel_scale_factor'])