Backport PR #3242: prevent spectral lines from converting y-range (#3266

)

Co-authored-by: Gilbert Green <42986583+gibsongreen@users.noreply.github.com>

CHANGES.rst

@@ -9,6 +9,9 @@ Bug Fixes
 - Fixed Aperture Photometry radial profile fit crashing when NaN is present in
   aperture data for Cubeviz and Imviz. [#3246]
 
+- Prevent PluginMarks from converting y-range so they maintain their position 
+  in the spectrum-viewer when spectral y units are converted. [#3242]
+
 Cubeviz
 ^^^^^^^
 

jdaviz/core/marks.py

@@ -157,6 +157,12 @@ def _on_global_display_unit_changed(self, msg):
             return
         axis = axis_map.get(msg.axis, None)
         if axis is not None:
+            scale = self.scales.get(axis, None)
+            # if PluginMark mark is LinearScale(0, 1), prevent it from entering unit conversion
+            # machinery so it maintains it's position in viewer.
+            if isinstance(scale, LinearScale) and (scale.min, scale.max) == (0, 1):
+                return
+
             getattr(self, f'set_{axis}_unit')(msg.unit)
 
     def clear(self):