NPI-3655 add remove_offline_sats from other codebase, to allow use in…

… general SP3 processing. Add option to remove offline sats when diffing SP3s, to avoid cubic velocity interpolator crashes. Add warning when using the cubic interpolator but not removing offline sats.

gnssanalysis/gn_io/sp3.py

@@ -191,6 +191,23 @@ def sp3_clock_nodata_to_nan(sp3_df: _pd.DataFrame) -> None:
     sp3_df.loc[nan_mask, ("EST", "CLK")] = _np.nan
 
 
+def remove_offline_sats(sp3_df: _pd.DataFrame):
+    """
+    Remove any satellites that have "0.0" for all three coordinates (i.e. nodata) - indicates satellite offline.
+    Note that this removes a satellite which has *any* missing coordinate data, meaning a satellite with partial
+    observations will get removed entirely.
+    Added in version 0.0.57
+    """
+    # Get all entries with missing coordinates (i.e. nodata, which would become NaN), then get the satellite
+    # names (SVs) of these and dedupe them, giving a list of all SVs with one or more missing coordinates.
+    offline_sats = (
+        sp3_df[(sp3_df.EST.X == 0.0) & (sp3_df.EST.Y == 0.0) & (sp3_df.EST.Z == 0.0)].index.get_level_values(1).unique()
+    )
+    sp3_df = sp3_df.drop(offline_sats, level=1, errors="ignore")
+    sp3_df.attrs["HEADER"].HEAD.ORB_TYPE = "INT"  # Allow the file to be read again by read_sp3 - File ORB_TYPE changes
+    return sp3_df
+
+
 def mapparm(old: Tuple[float, float], new: Tuple[float, float]) -> Tuple[float, float]:
     """
     Evaluate the offset and scale factor needed to map values from the old range to the new range.
@@ -454,6 +471,8 @@ def getVelSpline(sp3Df: _pd.DataFrame) -> _pd.DataFrame:
     :param DataFrame sp3Df: The input dataframe containing position data.
     :return DataFrame: The dataframe containing the velocity spline.
 
+    :caution :This function cannot handle *any* NaN / nodata / non-finite position values. By contrast, getVelPoly()
+              is more forgiving, but accuracy of results, particulary in the presence of NaNs, has not been assessed.
     :note :The velocity is returned in the same units as the input dataframe, e.g. km/s (needs to be x10000 to be in cm as per sp3 standard).
     """
     sp3dfECI = sp3Df.EST.unstack(1)[["X", "Y", "Z"]]  # _ecef2eci(sp3df)
@@ -849,14 +868,20 @@ def diff_sp3_rac(
     sp3_test: _pd.DataFrame,
     hlm_mode: Literal[None, "ECF", "ECI"] = None,
     use_cubic_spline: bool = True,
+    use_offline_sat_removal: bool = False,
 ) -> _pd.DataFrame:
     """
     Computes the difference between the two sp3 files in the radial, along-track and cross-track coordinates.
 
     :param DataFrame sp3_baseline: The baseline sp3 DataFrame.
     :param DataFrame sp3_test: The test sp3 DataFrame.
     :param string hlm_mode: The mode for HLM transformation. Can be None, "ECF", or "ECI".
-    :param bool use_cubic_spline: Flag indicating whether to use cubic spline for velocity computation.
+    :param bool use_cubic_spline: Flag indicating whether to use cubic spline for velocity computation. Caution: cubic
+           spline interpolation does not tolerate NaN / nodata values. Consider enabling use_offline_sat_removal if
+           using cubic spline, or alternatively use poly interpolation by setting use_cubic_spline to False.
+    :param bool use_offline_sat_removal: Flag indicating whether to remove satellites which are offline / have some
+           nodata position values. Caution: ensure you turn this on if using cubic spline interpolation with data
+           which may have holes in it (nodata).
     :return: The DataFrame containing the difference in RAC coordinates.
     """
     hlm_modes = [None, "ECF", "ECI"]
@@ -866,6 +891,20 @@ def diff_sp3_rac(
     # Drop any duplicates in the index
     sp3_baseline = sp3_baseline[~sp3_baseline.index.duplicated(keep="first")]
     sp3_test = sp3_test[~sp3_test.index.duplicated(keep="first")]
+
+    if use_cubic_spline and not use_offline_sat_removal:
+        logger.warning(
+            "Caution: use_cubic_spline is enabled, but use_offline_sat_removal is not. If there are any nodata "
+            "position values, the cubic interpolator will crash!"
+        )
+    # Drop any satellites (SVs) which are offline or partially offline.
+    # Note: this currently removes SVs with ANY nodata values for position, so a single glitch will remove
+    # the SV from the whole file.
+    # This step was added after velocity interpolation failures due to non-finite (NaN) values from offline SVs.
+    if use_offline_sat_removal:
+        sp3_baseline = remove_offline_sats(sp3_baseline)
+        sp3_test = remove_offline_sats(sp3_test)
+
     # Ensure the test file is time-ordered so when we align the resulting dataframes will be time-ordered
     sp3_baseline = sp3_baseline.sort_index(axis="index", level="J2000")
     sp3_baseline, sp3_test = sp3_baseline.align(sp3_test, join="inner", axis=0)