L2SS-554: Explained and simplified test for distance test

tangostationcontrol/tangostationcontrol/test/beam/test_delays.py

@@ -75,29 +75,27 @@ class TestDelays(base.TestCase):
 
     def test_light_second_delay(self):
         """
-        This test measures the delay between 2 positions 1 light second apart.
+        This test measures whether the distance between 2 positions is 0.1 light second apart.
         """
 
-        # # create a frame tied to the reference position
-        reference_itrf = [3826577.066, 461022.948, 5064892.786]  # CS002LBA, in ITRF2005 epoch 2012.5
         d = delay_calculator(reference_itrf)
 
-        # set the antenna position identical to the reference position
+        # set the antenna position 0.1 lightsecond in the Z direction of the ITRF,
+        # which is aligned with the North Pole, see
+        # https://en.wikipedia.org/wiki/Earth-centered,_Earth-fixed_coordinate_system#Structure
         speed_of_light = 299792458.0
-        antenna_itrf = [[reference_itrf[0], reference_itrf[1] - speed_of_light, reference_itrf[2]]]  # CS001LBA, in ITRF2005 epoch 2012.5
+        antenna_itrf = [[0, 0, 0.1 * speed_of_light]]
 
-        # # set the timestamp to solve for
-        timestamp = datetime.datetime(2000, 1, 1, 0, 0, 0)
+        # We need to point along the same direction in order to have the delay reflect the distance.
+        #
+        # We point at the North Celestial Pole in J2000, which is always at 90 degrees declanation,
+        # see https://gssc.esa.int/navipedia/index.php/Conventional_Celestial_Reference_System
+        timestamp = datetime.datetime(2022, 3, 1, 0, 0, 0) # timestamp does not actually matter, but casacore doesn't know that.
         d.set_measure_time(timestamp)
-
-        # compute the delays for an antennas w.r.t. the reference position
-
-        # # obtain the direction vector for a specific pointing
-        direction = "J2000", "0deg", "0deg"
+        direction = "J2000", "0deg", "90deg"
 
         # calculate the delays based on the set reference position, the set time and now the set direction and antenna positions.
         delays = d.convert(direction, antenna_itrf)
 
-
-        self.assertTrue(0.98 <= delays[0] <= 1.02, f"delays[0] = {delays[0]}")
+        self.assertAlmostEqual(0.1, delays[0], 6, f"delays[0] = {delays[0]}")