CLAUDE: fopen_pose_compare.py — add frame-numbering cross-reference docs

Documents the ImageJ (1-based slice:timestamp), INTERFRAME.corr-xml
(timestamp_microseconds key), and COLMAP (0-based frame_NNNN) conventions
in the module docstring so any frame can be cross-referenced across tools.
Also clarifies the underscore→dot timestamp conversion in parse_interframe_xml.
Co-authored-by: Claude <claude@elphel.com>

scripts/fopen_pose_compare.py

@@ -33,6 +33,21 @@ Output:
              delta-orientation RMSE (deg), top-10 worst frames
   - CSV (--out): per-frame positions, position residuals, absolute COLMAP & ERS
                  orientation angles in Sim(3)-aligned world frame, delta-angle diffs
+
+Frame numbering across systems
+-------------------------------
+ImageJ GUI shows slices 1-based with a timestamp label:
+    "47:1763233715_106222"   ← slice 47, timestamp 1763233715.106222 s
+
+*-INTERFRAME.corr-xml keys use the same timestamp with an underscore:
+    EYESIS_DCT_AUX.scenes_1763233715_106222
+
+COLMAP images.txt assigns 0-based sequential names (sorted by timestamp):
+    frame_0046.png           ← same scene; 0-based so ImageJ slice N = frame_N-1
+
+This script's CSV output keeps both the 0-based COLMAP 'frame' index and
+the float 'timestamp' so any frame can be cross-referenced unambiguously
+regardless of which sub-sequence was used (full 498 frames or a subset).
 """
 
 import argparse
@@ -218,7 +233,9 @@ def parse_interframe_xml(path, skip_rows=None):
             continue
         if len(vals) != 6:
             continue
-        # "1763233715_106222"  →  1763233715.106222
+        # Key suffix is "seconds_microseconds" with an underscore separator,
+        # e.g. "1763233715_106222" → 1763233715.106222 s (Unix-ish epoch).
+        # Replace only the first underscore so the integer part is preserved.
         ts_float = float(ts_str.replace("_", ".", 1))
         raw[ts_float] = vals