Generalize Linear Reduction

CHANGELOG.md

@@ -56,7 +56,7 @@ release.
 
 ### Changed
 - `isd_generate`: default `--reduction` to `linear` (sampling every 10th line for line-scan images with >= 1000 lines). This avoids creating oversized ISDs (tens of thousands of pose samples) for long line-scan sensors such as LRO NAC, MRO CTX, and HRSC. Pass `--reduction none` to disable reduction and restore per-line sampling. [#744](https://github.com/DOI-USGS/ale/pull/744)
-
+- Change the `linear` reduction option to apply to all drivers rather than just drivers built with the `LineScanner` mixin. [#752](https://github.com/DOI-USGS/ale/pull/752)
 ## [1.3.0] - 2026-08-25
 
 ### Added

ale/base/data_naif.py

@@ -23,6 +23,32 @@
 from ale import util
 from ale import ale_c
 
+def reduce_ephem(ephem_times, sample_rate, minimum=101):
+    """
+    Stand alone function to linearly reduce ephemeris times
+
+    Parameters
+    ----------
+    ephem_times : list
+        A list of ephemeris times to reduce over
+
+    sample_rate : int
+        The rate of sampling between the first and last time in
+        ephem_times
+
+    minimum : int
+        The minimum number of ephemeris times to not reduce
+        below
+    """
+    reduced = len(ephem_times) // sample_rate + 1
+    # Add check to avoid reducing below the minimum
+    if reduced < minimum:
+        logger.warning(f"Requested sampling of {sample_rate} would reduce total samples ({reduced}) below {minimum}. "
+                       f"Setting minimum sample size to {minimum}")
+        reduced = minimum
+    reduced_times = np.linspace(ephem_times[0], ephem_times[-1], reduced)
+    return reduced_times
+
 class NaifSpice():
     """
     Mix-in for reading data from NAIF SPICE Kernels.
@@ -193,7 +219,28 @@ def search_kernels(self):
             if self.use_web:
                 self._search_kernels = True
         return self._search_kernels
-
+
+    @property
+    def reduction(self):
+        """
+        Reduction property that reads a provided reduction method in the properties.
+
+        If no reduction is provided, or an unknown reduction is set reduction 
+        will be set to 'none' (no reduction)
+
+        Returns
+        -------
+        : str
+          The checked and defined reduction
+        """
+        if not hasattr(self, "_reduction"):
+            self._reduction = self._props.get('reduction', 'none').lower()
+            reduction_types = ["linear", "hermite", "none"]
+            if self._reduction not in reduction_types:
+                logger.warning(f"Unknown reduction value {self._reduction}, setting reduction to none")
+                self._reduction = "none"
+        return self._reduction
+
     @property
     def light_time_correction(self):
         """
@@ -543,7 +590,10 @@ def sensor_position(self):
            not hasattr(self, '_velocity') or \
            not hasattr(self, '_ephem'):
             logger.debug("Generating Sensor Positions")            
+            rate = self._props.get('ephem_sample_rate', 10)
             ephem = self.ephemeris_time
+            if self.reduction == 'linear' and len(ephem) != 1:
+                ephemeris_time = reduce_ephem(ephem, rate)
 
             pos = []
             vel = []
@@ -652,8 +702,7 @@ def sensor_position(self):
             self._velocity = np.asarray(vel)
             self._ephem = ephem
 
-            reduction = self._props.get('reduction', 'none').lower()
-            if reduction == 'hermite' and len(self._position) > 3:
+            if self.reduction == 'hermite' and len(self._position) > 3:
                 logger.debug("Applying hermite reduction to positions")
                 state_list = [ale_c.State(i) for i in np.append(self._position, self._velocity, axis=1)]
                 states = ale_c.StatesFromStateVec(self._ephem, state_list, 1)
@@ -710,13 +759,16 @@ def frame_chain(self):
         if not hasattr(self, '_frame_chain'):
             nadir = self._props.get('nadir', False)
             exact_ck_times = self._props.get('exact_ck_times', True)
-            reduction = self._props.get('reduction', 'none').lower()
+            rate = self._props.get('ephem_sample_rate', 10)
+            ephemeris_time = self.ephemeris_time
+            if self.reduction == 'linear' and len(ephemeris_time) != 1:
+                ephemeris_time = reduce_ephem(ephemeris_time, rate)
             self._frame_chain = FrameChain.from_spice(sensor_frame=self.sensor_frame_id,
                                                       target_frame=self.target_frame_id,
                                                       center_ephemeris_time=self.center_ephemeris_time,
-                                                      ephemeris_times=self.ephemeris_time,
+                                                      ephemeris_times=ephemeris_time,
                                                       nadir=nadir, exact_ck_times=exact_ck_times,
-                                                      reduction=reduction,
+                                                      reduction=self.reduction,
                                                       inst_time_bias=self.instrument_time_bias,
                                                       mission=self.spiceql_mission,
                                                       use_web=self.use_web,

ale/base/type_sensor.py

@@ -97,23 +97,7 @@ def ephemeris_time(self):
           ephemeris times split based on image lines
         """
         if not hasattr(self, "_ephemeris_time"):
-            # Determine reduction mode. Default is "None" (No reduction). 
-            # Set reduction=Linear via props to apply a linear reduction.
-            reduction = self._props.get('reduction', 'none').lower()
-
-            if reduction == 'linear':
-                # Sample at most every Nth line to keep ISD file size in check
-                # for large linescan images (e.g., 177k lines for Chandrayaan-2
-                # TMC). For images under ~1000 lines, keep one sample per line
-                # to avoid reducing below 100 samples.
-                rate = self._props.get('ephem_sample_rate', 10)
-                reduced = self.image_lines // rate + 1
-                num_samples = reduced if reduced >= 100 else self.image_lines + 1
-            else:
-                # No reduction
-                num_samples = self.image_lines + 1
-
-            self._ephemeris_time = np.linspace(self.ephemeris_start_time, self.ephemeris_stop_time, num_samples)
+            self._ephemeris_time = np.linspace(self.ephemeris_start_time, self.ephemeris_stop_time, self.image_lines + 1)
         return self._ephemeris_time
 
     @property

ale/drivers/chandrayaan_drivers.py

@@ -639,7 +639,7 @@ def sensor_frame_id(self):
         return self.original_naif_sensor_frame_id - 10
 
 class Chandrayaan2OHRCIsisLabelNaifSpiceDriver(LineScanner, IsisLabel, NaifSpice, NoDistortion, Driver):
-    
+
     @property
     def instrument_id(self):
         """
@@ -726,29 +726,25 @@ def ephemeris_stop_time(self):
         return self._ephemeris_stop_time
 
     @property
-    def ephemeris_time(self):
+    def reduction(self):
         """
-        Forces a reduced set of ephemeris data for chandrayaan2 as
-        many of the images are nearly 200K lines long resulting in
-        ISDs that cannot be loaded correctly into the CSM
+        Reduction property override that sets the default reduction to linear.
 
         Returns
         -------
-        : ndarray
-            ephemeris times split based on image lines and ephem_sample_rate passed
-            through props
-        """
-        if not hasattr(self, "_ephemeris_time"):
-            reduction = self._props.get('reduction', 'none').lower()
-            if (reduction == 'none'):
-                logger.warning("Chandrayaan-2 OHRC: per-line ephemeris ISDs are "
-                               "very large. Defaulting reduction to 'linear'. Pass "
-                               "--reduction linear --ephem_sample_rate N to control "
-                               "the sampling. An explicit --reduction none cannot be "
-                               "respected for this sensor.")
-                self._props['reduction'] = 'linear'
-            self._ephemeris_time = super().ephemeris_time
-        return self._ephemeris_time
+        : str
+          The checked and defined reduction
+        """
+        if not hasattr(self, "_reduction"):
+            self._reduction = super().reduction
+            if self._reduction == "none":
+                self._reduction = "linear"
+            logger.warning("Chandrayaan-2 OHRC: per-line ephemeris ISDs are "
+                           "very large. Defaulting reduction to 'linear'. Pass "
+                           "--reduction linear --ephem_sample_rate N to control "
+                           "the sampling. An explicit --reduction none cannot be "
+                           "respected for this sensor.")
+        return self._reduction
 
     @property
     def detector_center_line(self):

tests/pytests/conftest.py

@@ -60,7 +60,7 @@ def compare_dicts(ldict, rdict):
             differences.extend(compare_dicts(item, rdict[key]))
         elif isinstance(item, np.ndarray) or isinstance(item, list):
             if len(item) != len(rdict[key]):
-                differences.append(f'Array sizes of key {key} are not equal {item} : {rdict[key]}.')
+                differences.append(f'Array sizes of key {key} are not equal {len(item)} : {len(rdict[key])}.')
             else:
                 list_item = np.array(item).flat[0]
                 # quaternion (q) and its additive inverse (qi) yield the same rotation.  Equivalent quaternions should pass

tests/pytests/test_chandrayaan_driver.py

@@ -255,6 +255,9 @@ def setUp(self):
         label = get_image_label('ch2_ohr_nrp_20200827T0226453039_d_img_d18', 'isis3')
         self.driver = Chandrayaan2OHRCIsisLabelNaifSpiceDriver(label)
 
+    def test_default_reduction(self):
+        assert self.driver.reduction == "linear"
+
     def test_short_mission_name(self):
         assert self.driver.short_mission_name == 'chandrayaan'
 
@@ -285,12 +288,6 @@ def test_ephemeris_stop_time(self):
             calls = [call(utc='2020-08-27 02:27:01.687500', searchKernels=False, useWeb=False)]
             utcToEt.assert_has_calls(calls)
 
-    def test_ephemeris_time(self):
-        with patch("ale.drivers.chandrayaan_drivers.pyspiceql.utcToEt", return_value=[12345]) as utcToEt:
-            assert len(self.driver.ephemeris_time) == 10108
-            calls = [call(utc='2020-08-27 02:27:01.687500', searchKernels=False, useWeb=False)]
-            utcToEt.assert_has_calls(calls)
-
     def test_detector_center_sample(self):
         with patch.object(Chandrayaan2OHRCIsisLabelNaifSpiceDriver, 'naif_keywords', new_callable=PropertyMock) as naif_keywords_call:
             naif_keywords_call.return_value = {"INS-152270_CENTER": [2003.1, 3003.2]}

tests/pytests/test_data_naif.py

@@ -85,6 +85,9 @@ def test_detector_center_line(self):
     def test_swap_observer_target(self):
         assert not self.driver.swap_observer_target
 
+    def test_reduction(self):
+        assert self.driver.reduction == "none"
+
     def test_light_time_correction(self):
         assert self.driver.light_time_correction == "LT+S"