Clarify that loading a catalog for an existing catalog replaces the data

Author: mwcraig

src/astro_image_display_api/api_test.py

@@ -534,7 +534,7 @@ def test_load_catalog_multiple_same_label(self, catalog):
         self.image.load_catalog(catalog, catalog_label="test1")
 
         retrieved_catalog = self.image.get_catalog(catalog_label="test1")
-        assert len(retrieved_catalog) == 2 * len(catalog)
+        assert len(retrieved_catalog) == len(catalog)
 
     def test_load_catalog_with_skycoord_no_wcs(self, catalog, data):
         # Check that loading a catalog with skycoord but no x/y and

src/astro_image_display_api/image_viewer_logic.py

@@ -9,7 +9,7 @@
 from astropy import units as u
 from astropy.coordinates import SkyCoord
 from astropy.nddata import CCDData, NDData
-from astropy.table import Table, vstack
+from astropy.table import Table
 from astropy.units import Quantity
 from astropy.visualization import (
     AsymmetricPercentileInterval,
@@ -509,17 +509,8 @@ def load_catalog(
 
         catalog_label = self._resolve_catalog_label(catalog_label)
 
-        # Either set new data or append to existing data
-        if (
-            catalog_label in self._catalogs
-            and self._catalogs[catalog_label].data is not None
-        ):
-            # If the catalog already exists, we append to it
-            old_table = self._catalogs[catalog_label].data
-            self._catalogs[catalog_label].data = vstack([old_table, to_add])
-        else:
-            # If the catalog does not exist, we create a new one
-            self._catalogs[catalog_label].data = to_add
+        # Set the new data
+        self._catalogs[catalog_label].data = to_add
 
         # Ensure a catalog always has a style
         if catalog_style is None:

src/astro_image_display_api/interface_definition.py

@@ -345,6 +345,9 @@ def load_catalog(
         """
         Add catalog entries to the viewer at positions given by the catalog.
 
+        Loading a catalog using a ``catalog_label`` that already exists will
+        overwrite the existing catalog with the new one.
+
         Parameters
         ----------
         table : `astropy.table.Table`