From 6bcb91a660ff188220338fb8523cf95e6a2c28f3 Mon Sep 17 00:00:00 2001
From: Maxine Hartnett <maxine.hartnett@lasp.colorado.edu>
Date: Wed, 1 Apr 2026 13:55:21 -0600
Subject: [PATCH] Revert "A rotated NaN is still a NaN (#2901)"

This reverts commit cdfd0aeddc390c0129b1cf75f97176126597f305.
---
 imap_processing/spice/geometry.py            | 10 ----------
 imap_processing/tests/spice/test_geometry.py | 20 --------------------
 2 files changed, 30 deletions(-)

diff --git a/imap_processing/spice/geometry.py b/imap_processing/spice/geometry.py
index 1d7b11988..132560932 100644
--- a/imap_processing/spice/geometry.py
+++ b/imap_processing/spice/geometry.py
@@ -18,8 +18,6 @@
 import spiceypy
 from numpy.typing import NDArray
 
-from imap_processing.mag import constants
-
 logger = logging.getLogger(__name__)
 
 
@@ -319,14 +317,6 @@ def frame_transform(
     # Multiple et/positions :  (n, 3, 3),(n, 3, 1) -> (n, 3, 1)
     result = np.squeeze(rotate @ position[..., np.newaxis])
 
-    # For every FILLVAL in the input position, ensure the output is also NaN or FILLVAL
-    if np.isnan(position).any() or (position == constants.FILLVAL).any():
-        result = np.where(
-            np.isnan(position) | (position == constants.FILLVAL),
-            constants.FILLVAL,
-            result,
-        )
-
     return result
 
 
diff --git a/imap_processing/tests/spice/test_geometry.py b/imap_processing/tests/spice/test_geometry.py
index 19774e198..8e0465ba0 100644
--- a/imap_processing/tests/spice/test_geometry.py
+++ b/imap_processing/tests/spice/test_geometry.py
@@ -6,7 +6,6 @@
 import pytest
 import spiceypy
 
-from imap_processing.mag import constants
 from imap_processing.spice.geometry import (
     SpiceBody,
     SpiceFrame,
@@ -160,19 +159,6 @@ def test_get_spacecraft_to_instrument_spin_phase_offset(
             SpiceFrame.IMAP_SPACECRAFT,
             SpiceFrame.IMAP_DPS,
         ),
-        # single et, single NaN/FILL_VAL vector
-        (
-            ["2025-04-30T12:00:00.000"],
-            np.array(
-                [
-                    [0, 0, 0],
-                    [constants.FILLVAL, constants.FILLVAL, constants.FILLVAL],
-                    [np.nan, np.nan, np.nan],
-                ]
-            ),
-            SpiceFrame.IMAP_SPACECRAFT,
-            SpiceFrame.IMAP_DPS,
-        ),
     ],
 )
 def test_frame_transform(et_strings, position, from_frame, to_frame, furnish_kernels):
@@ -217,12 +203,6 @@ def test_frame_transform(et_strings, position, from_frame, to_frame, furnish_ker
             spice_result = spiceypy.mxv(rotation_matrix, spice_position)
             np.testing.assert_allclose(test_result, spice_result, atol=1e-12)
 
-        # Ensure that NaN/FILL_VAL inputs are preserved exactly as FILL_VAL outputs
-        # and not just really close to but not quite FILL_VAL
-        for input_vec, output_vec in zip(position, result, strict=False):
-            if np.isnan(input_vec).all() or (input_vec == constants.FILLVAL).all():
-                assert (output_vec == constants.FILLVAL).all()
-
 
 @pytest.mark.parametrize(
     "spice_frame",