Repository: yt-project/yt

Issue:
Off axis Slice Plot breaks when using derived field and default center 
<!--To help us understand and resolve your issue, please fill out the form to
the best of your ability.-->
<!--You can feel free to delete the sections that do not apply.-->

### Bug report

**Bug summary**

Creating an `OffAxisSlicePlot` with a derived field (e.g. `('gas', 'radial_velocity')` yields an error unless the center is defined (e.g. `center=ds.domain_center`). 

**Code for reproduction**
Using IsolatedGalaxy dataset

```python
import yt

ds = yt.load("IsolatedGalaxy/galaxy0030/galaxy0030")
yt.SlicePlot(ds, [0.5, 0., 0.5], ("gas", "radial_velocity"))
```

**Actual outcome**

<!--The output produced by the above code, which may be a screenshot, console
output, etc.-->

```
Traceback (most recent call last):
  File "/home/biboyd/workspace/yt_bug_fix/test_yt.py", line 4, in <module>
    yt.SlicePlot(ds, [0.5, 0., 0.5], ("gas", "radial_velocity"))
  File "/home/biboyd/Repo/my_yt/yt/visualization/plot_window.py", line 2238, in __init__
    cutting.get_data(fields)
  File "/home/biboyd/Repo/my_yt/yt/data_objects/selection_objects/data_selection_objects.py", line 220, in get_data
    self._generate_fields(fields_to_generate)
  File "/home/biboyd/Repo/my_yt/yt/data_objects/selection_objects/data_selection_objects.py", line 252, in _generate_fields
    fd = self._generate_field(field)
  File "/home/biboyd/Repo/my_yt/yt/data_objects/data_containers.py", line 273, in _generate_field
    tr = self._generate_fluid_field(field)
  File "/home/biboyd/Repo/my_yt/yt/data_objects/data_containers.py", line 291, in _generate_fluid_field
    rv = finfo(gen_obj)
  File "/home/biboyd/Repo/my_yt/yt/fields/derived_field.py", line 285, in __call__
    dd = self._function(self, data)
  File "/home/biboyd/Repo/my_yt/yt/fields/geometric_fields.py", line 175, in _spherical_theta
    coords = get_periodic_rvec(data)
  File "/home/biboyd/Repo/my_yt/yt/fields/field_functions.py", line 47, in get_periodic_rvec
    coords = obtain_position_vector(data).d
  File "yt/utilities/lib/misc_utilities.pyx", line 586, in yt.utilities.lib.misc_utilities.obtain_position_vector
AttributeError: 'str' object has no attribute 'to'
```

**Expected outcome**

Expected a Slice

**Version Information**

  * Operating System: Ubuntu 22.04
  * Python Version: 3.10.12
  * yt version: 4.4.dev0 Changeset = c148f7264577
  * Other Libraries (if applicable):

yt installed from source


Discussion:

Resolving patch:
diff --git a/yt/data_objects/selection_objects/slices.py b/yt/data_objects/selection_objects/slices.py
--- a/yt/data_objects/selection_objects/slices.py
+++ b/yt/data_objects/selection_objects/slices.py
@@ -214,7 +214,7 @@ def __init__(
         validate_object(data_source, YTSelectionContainer)
         YTSelectionContainer2D.__init__(self, None, ds, field_parameters, data_source)
         self._set_center(center)
-        self.set_field_parameter("center", center)
+        self.set_field_parameter("center", self.center)
         # Let's set up our plane equation
         # ax + by + cz + d = 0
         self.orienter = Orientation(normal, north_vector=north_vector)


Test patch: