CLAUDE: fopen_turn_finder.py — add AGL from elevations_histogram.csv

*-elevations_histogram.csv (row 2, col 1) gives flight altitude above
ground level for each sequence.  Low AGL (<25-50 m) correlates with
algorithm failures in dense-canopy areas.

Changes:
- find_xml_files: also yields hist_path (*-elevations_histogram.csv)
- parse_agl(): reads AGL from second row, first column (tab-separated)
- agl_m added to sequence metrics dict and TSV output
- --min_agl filter: hide sequences below given AGL from console output
- AGL column shown in console tables
Co-authored-by: Claude <claude@elphel.com>

scripts/fopen_turn_finder.py

@@ -197,9 +197,12 @@ def sequence_metrics(pose_arr, dt_arr):
 
 def find_xml_files(root):
     """
-    Yield (scene_ts_str, xml_path) for every scene directory under root.
-    Picks the latest version subdirectory by name (e.g. v88 > v80).
+    Yield (scene_ts_str, xml_path, hist_path_or_None) for every scene dir
+    under root.  Picks the latest version subdirectory by name (e.g. v88 > v80).
     Skips directories whose name ends with '-index'.
+
+    hist_path is the *-elevations_histogram.csv inside the version subdir,
+    or None if not present.
     """
     try:
         scene_dirs = sorted(os.listdir(root))
@@ -225,10 +228,32 @@ def find_xml_files(root):
             continue
         ver = sorted(subdirs)[-1]
 
-        ver_path = os.path.join(scene_path, ver)
-        xml_path = os.path.join(ver_path, f"{scene}-INTERFRAME.corr-xml")
+        ver_path  = os.path.join(scene_path, ver)
+        xml_path  = os.path.join(ver_path, f"{scene}-INTERFRAME.corr-xml")
+        hist_path = os.path.join(ver_path, f"{scene}-elevations_histogram.csv")
         if os.path.isfile(xml_path):
-            yield scene, xml_path
+            yield scene, xml_path, (hist_path if os.path.isfile(hist_path) else None)
+
+
+def parse_agl(hist_path):
+    """
+    Read AGL (flight altitude above ground level, metres) from
+    *-elevations_histogram.csv.
+
+    Format:
+      Row 1 (header): AGL  ELEVATION  FRACTION_LOWER
+      Row 2:          <agl_value>  <elev>  <frac>   ← AGL is here
+      Row 3+:         (empty first col, cumulative histogram continues)
+
+    Returns float AGL, or nan if the file cannot be parsed.
+    """
+    try:
+        with open(hist_path) as f:
+            next(f)                       # skip header
+            first_data = next(f).split('\t')
+            return float(first_data[0])
+    except Exception:
+        return float('nan')
 
 
 # ─────────────────────────────── main ────────────────────────────────────── #
@@ -248,17 +273,21 @@ def main():
     ap.add_argument('--max_glitch', type=float, default=None,
                     help='Hide sequences whose R glitch ratio exceeds this '
                          '(e.g. 5.0 keeps only clean data; default: show all)')
+    ap.add_argument('--min_agl',   type=float, default=None,
+                    help='Hide sequences with AGL below this value in metres '
+                         '(e.g. 50 skips low-altitude failure-prone sequences)')
     args = ap.parse_args()
 
     print(f"Scanning {args.root} …", flush=True)
     rows = []
-    for scene_ts, xml_path in find_xml_files(args.root):
+    for scene_ts, xml_path, hist_path in find_xml_files(args.root):
         pose_arr, dt_arr = parse_xml(xml_path)
         if pose_arr is None:
             continue
         m = sequence_metrics(pose_arr, dt_arr)
         m['scene_ts'] = scene_ts
         m['xml_path'] = xml_path
+        m['agl_m']    = parse_agl(hist_path) if hist_path else float('nan')
         rows.append(m)
 
     print(f"Parsed {len(rows)} sequences.", flush=True)
@@ -275,18 +304,24 @@ def main():
     }
     sort_key = sort_map[args.sort]
 
-    # apply glitch filter
+    # apply filters
     display = rows
     if args.max_glitch is not None:
-        display = [r for r in rows
+        display = [r for r in display
                    if (r.get('r_glitch') or 0) <= args.max_glitch]
         print(f"After glitch filter (r_glitch ≤ {args.max_glitch}): "
               f"{len(display)} sequences remain.")
+    if args.min_agl is not None:
+        display = [r for r in display
+                   if np.isfinite(r.get('agl_m', float('nan')))
+                   and r['agl_m'] >= args.min_agl]
+        print(f"After AGL filter (≥ {args.min_agl} m): "
+              f"{len(display)} sequences remain.")
 
     display.sort(key=lambda r: r.get(sort_key) or 0, reverse=True)
 
     # ── console report ────────────────────────────────────────────────────
-    hdr = (f"  {'Scene':>22}  {'fr':>4}  {'range(°)':>8}  "
+    hdr = (f"  {'Scene':>22}  {'fr':>4}  {'AGL(m)':>7}  {'range(°)':>8}  "
            f"{'dt_max(°/s)':>11}  {'at timestamp':>20}  "
            f"{'glitch':>7}  {'fd_max(°/s)':>11}")
 
@@ -302,7 +337,9 @@ def main():
         print(f"{'═'*90}")
         print(hdr)
         for r in ranked[:args.top]:
-            print(f"  {r['scene_ts']:>22}  {r['n_frames']:>4}  "
+            agl = r.get('agl_m', float('nan'))
+            agl_s = f"{agl:7.1f}" if np.isfinite(agl) else "    n/a"
+            print(f"  {r['scene_ts']:>22}  {r['n_frames']:>4}  {agl_s}  "
                   f"{r[f'{axis}_range(deg)']:>8.2f}  "
                   f"{r[f'{axis}_dt_max(deg/s)']:>11.3f}  "
                   f"{r[f'{axis}_dt_ts']:>20.3f}  "
@@ -312,7 +349,7 @@ def main():
     # ── TSV output ────────────────────────────────────────────────────────
     if args.out:
         fieldnames = [
-            'scene_ts', 'n_frames', 'duration_s',
+            'scene_ts', 'n_frames', 'duration_s', 'agl_m',
             'r_dt_max(deg/s)', 'r_dt_ts', 'r_range(deg)', 'r_glitch', 'r_fd_max(deg/s)',
             't_dt_max(deg/s)', 't_dt_ts', 't_range(deg)', 't_glitch', 't_fd_max(deg/s)',
             'a_dt_max(deg/s)', 'a_dt_ts', 'a_range(deg)', 'a_glitch', 'a_fd_max(deg/s)',