NPI-3668 small clarifying comments

gnssanalysis/gn_io/sp3.py

@@ -325,7 +325,7 @@ def read_sp3(
     header = content[:header_end]
     content = content[header_end:]
     parsed_header = parse_sp3_header(header)
-    header_sv_count = parsed_header.SV_INFO.count()
+    header_sv_count = parsed_header.SV_INFO.count()  # count() of non-NA/null, vs shape: dims of whole structure
     fline_b = header.find(b"%f") + 2  # TODO add to header parser
     fline = header[fline_b : fline_b + 24].strip().split(b"  ")
     base_xyzc = _np.asarray([float(fline[0])] * 3 + [float(fline[1])])  # exponent base
@@ -440,7 +440,7 @@ def parse_sp3_header(header: bytes, warn_on_negative_sv_acc_values: bool = True)
     head_svs = _np.asarray(sv_id_matches)[_np.newaxis].view("S3").astype(str)
 
     # Sanity check that the number of SVs the regex found, matches what the header said should be there.
-    found_sv_count = head_svs.shape[0]  # Effectively len() of the SVs array.
+    found_sv_count = head_svs.shape[0]  # Effectively len() of the SVs array. Note this could include null/NA/NaN
     if head_sv_expected_count is not None and found_sv_count != head_sv_expected_count:
         logger.warning(
             "Number of Satellite Vehicle (SV) entries extracted from the SP3 header, did not match the "

tests/test_sp3.py

@@ -228,6 +228,7 @@ def test_sp3merge(self):
             34,
             "Header stated count of SVs should be 34, matching actual number of SVs",
         )
+        # Note: shape of first dimension (unlike count() where applicable) could include null/NA/NaN
         self.assertEqual(result.attrs["HEADER"].SV_INFO.shape[0], 34, "Union of SV lists should have 34 SVs in it")
         # Sample first three orbit accuracy codes and ensure that for each SV, the accuracy code value is the
         # *worst* seen across all inputs. I.e. lowest common denominator of input files.