Redshift alignment for simple rays

trident/light_ray.py

@@ -311,11 +311,11 @@ def _calculate_light_ray_solution(self, seed=None,
     def make_light_ray(self, seed=None, periodic=True,
                        left_edge=None, right_edge=None, min_level=None,
                        start_position=None, end_position=None,
-                       trajectory=None,
-                       fields=None, setup_function=None,
+                       trajectory=None, fields=None, setup_function=None,
                        solution_filename=None, data_filename=None,
                        get_los_velocity=None, use_peculiar_velocity=True,
-                       redshift=None, field_parameters=None, njobs=-1):
+                       redshift=None, redshift_align=None,
+                       field_parameters=None, njobs=-1):
         """
         Actually generate the LightRay by traversing the desired dataset.
 
@@ -419,7 +419,19 @@ def make_light_ray(self, seed=None, periodic=True,
             redshift will be 0 for a non-cosmological dataset and
             the dataset redshift for a cosmological dataset.
             Default: None.
-
+
+        :redshift_align: optional, str
+
+            Used with light rays with single datasets to specify where the
+            redshift is "equal" to the redshift of the dataset, or "redshift"
+            if that was specified. If "start" or None, the line start will be
+            at this redshift and the line end will be at a lower redshift.
+            Other options are "center", so the line start will be greater than
+            this redshift, the line end will be less, and they will align at the
+            midpoint, and "everywhere", so the line will be at this redshift
+            throughout.
+            Default: None.
+
         :field_parameters: optional, dict
             Used to set field parameters in light rays. For example,
             if the 'bulk_velocity' field parameter is set, the relative
@@ -517,13 +529,14 @@ def make_light_ray(self, seed=None, periodic=True,
         self._data = {}
         # temperature field is automatically added to fields
         if fields is None: fields = []
-        if ('gas', 'temperature') not in fields:
-           fields.append(('gas', 'temperature'))
+        if (('gas', 'temperature') not in fields) and \
+           ('temperature' not in fields):
+            fields.append(('gas', 'temperature'))
         data_fields = fields[:]
         all_fields = fields[:]
         all_fields.extend(['l', 'dl', 'redshift'])
-        all_fields.extend(['x', 'y', 'z'])
-        data_fields.extend(['x', 'y', 'z'])
+        all_fields.extend([('gas','x'),('gas','y'),('gas','z')])
+        data_fields.extend([('gas','x'),('gas','y'),('gas','z')])
         if use_peculiar_velocity:
             all_fields.extend(['relative_velocity_x', 'relative_velocity_y',
                                'relative_velocity_z',
@@ -552,7 +565,10 @@ def make_light_ray(self, seed=None, periodic=True,
                     mylog.warning("Generating light ray with different redshift than " +
                                   "the dataset itself.")
                 my_segment["redshift"] = redshift
-
+
+            if redshift_align is None:
+                redshift_align = 'start'
+
             if setup_function is not None:
                 setup_function(ds)
 
@@ -567,8 +583,8 @@ def make_light_ray(self, seed=None, periodic=True,
                     segment_length = my_segment["traversal_box_fraction"] * \
                       ds.domain_width[0].in_units("Mpccm / h")
                 next_redshift = my_segment["redshift"] - \
-                  self._deltaz_forward(my_segment["redshift"],
-                                       segment_length)
+                    self._deltaz_forward(my_segment["redshift"],
+                                                segment_length)
             elif my_segment.get("next", None) is None:
                 next_redshift = self.near_redshift
             else:
@@ -675,10 +691,26 @@ def make_light_ray(self, seed=None, periodic=True,
                 sub_data[key] = ds.arr(sub_data[key]).in_cgs()
 
             # Get redshift for each lixel.  Assume linear relation between l
-            # and z.  so z = z_start - z_range * (l / l_range)
-            sub_data[('gas', 'redshift')] = my_segment['redshift'] - \
-              (sub_data[('gas', 'l')] / ray_length) * \
-              (my_segment['redshift'] - next_redshift)
+            # and z, depending on where they should be "aligned".
+            # 'start':      z = z_dataset - z_range * (l / l_range)
+            # 'center':     z = z_dataset - z_range * ((l - l_range/2) / l_range)
+            # 'everywhere': z = z_dataset
+            if redshift_align == 'start':
+                sub_data[('gas','redshift')] = my_segment['redshift'] - \
+                  (sub_data[('gas','l')] / ray_length) * \
+                  (my_segment['redshift'] - next_redshift)
+            elif redshift_align == 'center':
+                sub_data[('gas','redshift')] = my_segment['redshift'] - \
+                  ((sub_data[('gas','l')]-ray_length/2) / ray_length) * \
+                  (my_segment['redshift'] - next_redshift)
+            elif redshift_align == 'everywhere':
+                sub_data[('gas','redshift')] = np.ones(sub_data[('gas','l')].shape)*\
+                  my_segment['redshift']
+            else:
+                mylog.warning(f'redshift_align {redshift_align} not recognized. '+\
+                              'Using z = z_start for full length')
+                sub_data[('gas','redshift')] = np.ones(sub_data[('gas','l')].shape)*\
+                  my_segment['redshift']
 
             # When using the peculiar velocity, create effective redshift
             # (redshift_eff) field combining cosmological redshift and

trident/ray_generator.py

@@ -30,7 +30,8 @@
 def make_simple_ray(dataset_file, start_position, end_position,
                     lines=None, ftype="gas", fields=None,
                     solution_filename=None, data_filename=None,
-                    trajectory=None, redshift=None, field_parameters=None,
+                    trajectory=None, redshift=None,
+                    redshift_align='start', field_parameters=None,
                     setup_function=None, load_kwargs=None,
                     line_database=None, ionization_table=None):
     """
@@ -124,10 +125,19 @@ def make_simple_ray(dataset_file, start_position, end_position,
 
     :redshift: float, optional
 
-        Sets the highest cosmological redshift of the ray.  By default, it will
+        Sets the base cosmological redshift of the ray.  By default, it will
         use the cosmological redshift of the dataset, if set, and if not set,
         it will use a redshift of 0.
         Default: None
+
+    :redshift_align: optional, str
+
+        Sets the location where the cosmological redshift "aligns" with the base
+        cosmological redshift. Default is the start of the ray, other options are
+        'center', so the start will be higher redshift and the end will be lower,
+        and 'everywhere', so the full length will be at the base cosmological
+        redshift
+        Default: 'start'
 
     :field_parameters: optional, dict
         Used to set field parameters in light rays. For example,
@@ -231,7 +241,8 @@ def make_simple_ray(dataset_file, start_position, end_position,
                              solution_filename=solution_filename,
                              data_filename=data_filename,
                              field_parameters=field_parameters,
-                             redshift=redshift)
+                             redshift=redshift,
+                             redshift_align=redshift_align)
 
 def make_compound_ray(parameter_filename, simulation_type,
                       near_redshift, far_redshift,