Fix the error_ellipse calculation.

CHANGELOG.md

@@ -19,6 +19,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 #### Fixed
 
+- Fixed incorrect error ellipse calculation [#792](https://github.com/askap-vast/vast-pipeline/pull/792)
 - Renamed variable in pipeline.finalise to better reflect what the dataframe represents (sources_df -> associations_df) [#787](https://github.com/askap-vast/vast-pipeline/pull/787)
 - Fixed typo in variable name ("assoications") [#787](https://github.com/askap-vast/vast-pipeline/pull/787)
 - Fix processing config parameters not displaying in web interface [#782](https://github.com/askap-vast/vast-pipeline/pull/782)
@@ -28,6 +29,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 #### List of PRs
 
+- [#792](https://github.com/askap-vast/vast-pipeline/pull/792): fix: Simplify and correct error ellipse calculation.
 - [#788](https://github.com/askap-vast/vast-pipeline/pull/788): feat, fix: Speed up forced fitting code by using numba-fied forced_phot code and reordering some calculations
 - [#787](https://github.com/askap-vast/vast-pipeline/pull/787): fix: Optimise associations merge and minor variable name updates
 - [#782](https://github.com/askap-vast/vast-pipeline/pull/782): fix: Fix processing config parameters not displaying in web interface

vast_pipeline/image/main.py

@@ -14,7 +14,6 @@
 from astropy.wcs.utils import proj_plane_pixel_scales
 from typing import Dict
 
-from .utils import calc_error_radius
 from .utils import calc_condon_flux_errors
 
 from vast_pipeline import models
@@ -436,11 +435,14 @@ def read_selavy(self, dj_image: models.Image) -> pd.DataFrame:
         df['ew_sys_err'] = self.config["ra_uncertainty"] / 3600.
         df['ns_sys_err'] = self.config["dec_uncertainty"] / 3600.
 
-        df['error_radius'] = calc_error_radius(
-            df['ra'].values,
-            df['ra_err'].values,
-            df['dec'].values,
-            df['dec_err'].values,
+        # NOTE: The simplified error_radius calculation
+        # computed here is a replacement for the erroneous
+        # implementation in the calc_error_radius function
+        # in utils.py. It should mimic the intended functionality
+        # of that function as well as the implementation
+        # in TraP.
+        df['error_radius'] = np.hypot(
+            df['ra_err'].values, df['dec_err'].values
         )
 
         df['uncertainty_ew'] = np.hypot(

vast_pipeline/tests/test_regression/test_epoch.py

@@ -225,7 +225,7 @@ def test_num_sources(self):
         '''
         See documentation for test_num_sources in property_check.
         '''
-        property_check.test_num_sources(self, self.sources, 616)
+        property_check.test_num_sources(self, self.sources, 609)
 
     def test_most_relations(self):
         '''

vast_pipeline/tests/test_regression/test_epoch_forced.py

@@ -286,4 +286,4 @@ def test_forced_num(self):
         See documentation for test_forced_num in property_check.
         '''
         property_check.test_forced_num(
-            self, self.forced, 982)
+            self, self.forced, 961)

vast_pipeline/tests/test_regression/test_epoch_parallel_add_image.py

@@ -275,7 +275,7 @@ def test_num_sources(self):
         '''
         See documentation for test_num_sources in property_check.
         '''
-        property_check.test_num_sources(self, self.sources, 617)
+        property_check.test_num_sources(self, self.sources, 610)
 
     def test_most_relations(self):
         '''

vast_pipeline/tests/test_regression/test_normal.py

@@ -225,7 +225,7 @@ def test_num_sources(self):
         '''
         See documentation for test_num_sources in property_check.
         '''
-        property_check.test_num_sources(self, self.sources, 618)
+        property_check.test_num_sources(self, self.sources, 611)
 
     def test_most_relations(self):
         '''