sky plot: add per-satellite trajectory trails

- Store up to 1 hour of (elevation, azimuth) history per satellite/source
- Trail column in satellite table (checkbox, default off); clicking the
  column header toggles all trails on/off
- Trail rendered in GNSS color with alpha fading from 15 (oldest) to 200
  (newest), subsampled to max 120 points for render performance
- Trail column fixed at 42 px to avoid checkbox + empty-text visual split

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

gui/sky_tab.py

@@ -1,4 +1,5 @@
-import sys, os
+import sys, os, time
+from collections import deque
 
 _root = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 _gui  = os.path.dirname(os.path.abspath(__file__))
@@ -17,18 +18,22 @@ from PyQt5.QtGui  import QColor, QBrush
 from data_model import ReceiverManager, GNSS_NAMES, GNSS_COLORS
 from sky_widget import SkyPlotWidget
 
-_COL_HEADERS = ['GNSS', 'SV', 'Elev °', 'Az °', 'C/N₀', 'Fix', 'Receiver']
+_COL_HEADERS  = ['GNSS', 'SV', 'Elev °', 'Az °', 'C/N₀', 'Fix', 'Receiver', 'Trail']
+_COL_TRAIL    = len(_COL_HEADERS) - 1
+_TRAIL_MAXLEN = 3600   # 1 hour at 1 Hz
 
 
 class SkyTab(QWidget):
     def __init__(self, model: ReceiverManager):
         super().__init__()
         self._model = model
-        self._store:       dict = {}   # (rid, gnss_id, sv_id) -> SatelliteData
+        self._store:         dict = {}   # (rid, gnss_id, sv_id) -> SatelliteData
-        self._table_keys:  list = []   # current row order as (rid, gnss_id, sv_id)
+        self._table_keys:    list = []   # current row order as (rid, gnss_id, sv_id)
-        self._pdop:        dict = {}   # rid -> float
+        self._pdop:          dict = {}   # rid -> float
-        self._info_cards:  dict = {}   # rid -> QFrame
+        self._info_cards:    dict = {}   # rid -> QFrame
-        self._info_labels: dict = {}   # rid -> (lbl_pdop, lbl_visible, lbl_used)
+        self._info_labels:   dict = {}   # rid -> (lbl_pdop, lbl_visible, lbl_used)
+        self._trail:         dict = {}   # (rid, gnss_id, sv_id) -> deque[(elev, azim)]
+        self._trail_enabled: dict = {}   # (rid, gnss_id, sv_id) -> bool
 
         outer = QVBoxLayout(self)
         outer.setContentsMargins(4, 4, 4, 4)
@@ -66,11 +71,18 @@ class SkyTab(QWidget):
         self._table = QTableWidget()
         self._table.setColumnCount(len(_COL_HEADERS))
         self._table.setHorizontalHeaderLabels(_COL_HEADERS)
-        self._table.horizontalHeader().setSectionResizeMode(QHeaderView.ResizeToContents)
+        hdr = self._table.horizontalHeader()
-        self._table.horizontalHeader().setStretchLastSection(True)
+        hdr.setSectionResizeMode(QHeaderView.ResizeToContents)
+        hdr.setSectionResizeMode(_COL_TRAIL, QHeaderView.Fixed)
+        hdr.setStretchLastSection(False)
+        hdr.sectionClicked.connect(self._on_header_clicked)
+        self._table.setColumnWidth(_COL_TRAIL, 42)
+        self._table.horizontalHeader().setToolTip(
+            "Click 'Trail' header to select / deselect all")
         self._table.setEditTriggers(QTableWidget.NoEditTriggers)
         self._table.setSelectionBehavior(QTableWidget.SelectRows)
         self._table.setAlternatingRowColors(False)
+        self._table.itemChanged.connect(self._on_table_item_changed)
         splitter.addWidget(self._table)
 
         splitter.setStretchFactor(0, 2)
@@ -89,7 +101,7 @@ class SkyTab(QWidget):
         model.satellite_update.connect(self._on_sat_update)
         model.pdop_update.connect(self._on_pdop_update)
 
-    # ── Source list management ────────────────────────────────────────────────
+    # ── Source list management ───────────────────────────────────────────���────
 
     def _on_receiver_added(self, rid: str):
         item = QListWidgetItem(f"  {rid}  ")
@@ -98,13 +110,12 @@ class SkyTab(QWidget):
         item.setData(Qt.UserRole, rid)
         self._src_list.addItem(item)
 
-        # Info card for this receiver
         card = QFrame()
         card.setFrameShape(QFrame.Box)
         cl = QHBoxLayout(card)
         cl.setContentsMargins(8, 1, 8, 1)
         cl.setSpacing(10)
-        name_lbl = QLabel(f"<b>{rid}</b>")
+        name_lbl    = QLabel(f"<b>{rid}</b>")
         lbl_pdop    = QLabel("pDOP: —")
         lbl_visible = QLabel("Visible: —")
         lbl_used    = QLabel("Used: —")
@@ -119,9 +130,9 @@ class SkyTab(QWidget):
             if self._src_list.item(i).data(Qt.UserRole) == rid:
                 self._src_list.takeItem(i)
                 break
-        keys = [k for k in self._store if k[0] == rid]
+        for k in [k for k in self._store         if k[0] == rid]: del self._store[k]
-        for k in keys:
+        for k in [k for k in self._trail         if k[0] == rid]: del self._trail[k]
-            del self._store[k]
+        for k in [k for k in self._trail_enabled if k[0] == rid]: del self._trail_enabled[k]
         self._pdop.pop(rid, None)
         card = self._info_cards.pop(rid, None)
         if card:
@@ -143,6 +154,14 @@ class SkyTab(QWidget):
         return [(k[0], self._store[k])
                 for k in self._store if k[0] in selected]
 
+    def _active_trails(self) -> dict:
+        selected = self._selected_rids()
+        result   = {}
+        for key, dq in self._trail.items():
+            if key[0] in selected and self._trail_enabled.get(key, False):
+                result[key] = list(dq)
+        return result
+
     # ── Info bar ──────────────────────────────────────────────────────────────
 
     def _update_info(self):
@@ -159,8 +178,13 @@ class SkyTab(QWidget):
 
     def _on_sat_update(self, rid: str, sats: list):
         for sat in sats:
-            self._store[(rid, sat.gnss_id, sat.sv_id)] = sat
+            key = (rid, sat.gnss_id, sat.sv_id)
-        self._sky.update_data(self._visible_sats())
+            self._store[key] = sat
+            if key not in self._trail:
+                self._trail[key] = deque(maxlen=_TRAIL_MAXLEN)
+            self._trail[key].append((sat.elevation, sat.azimuth))
+
+        self._sky.update_data(self._visible_sats(), self._active_trails())
         self._update_info()
         if not self._table_timer.isActive():
             self._table_timer.start()
@@ -170,41 +194,77 @@ class SkyTab(QWidget):
         self._update_info()
 
     def _refresh_immediate(self):
-        """Called on source-checkbox toggle or receiver removal — rebuild now."""
         self._table_timer.stop()
         visible = self._visible_sats()
-        self._sky.update_data(visible)
+        self._sky.update_data(visible, self._active_trails())
         self._update_info()
         self._rebuild_table(visible)
 
     def _rebuild_table_from_store(self):
         self._rebuild_table(self._visible_sats())
 
+    # ── Trail toggle ──────────────────────────────────────────────────────────
+
+    def _on_table_item_changed(self, item):
+        if item.column() != _COL_TRAIL:
+            return
+        key = item.data(Qt.UserRole)
+        if key is None:
+            return
+        self._trail_enabled[key] = (item.checkState() == Qt.Checked)
+        self._sky.update_data(self._visible_sats(), self._active_trails())
+
+    def _on_header_clicked(self, col: int):
+        if col != _COL_TRAIL:
+            return
+        # Enable all if any are off, otherwise disable all
+        rows = self._table.rowCount()
+        any_off = any(
+            self._table.item(r, _COL_TRAIL).checkState() != Qt.Checked
+            for r in range(rows)
+            if self._table.item(r, _COL_TRAIL)
+        )
+        new_state = Qt.Checked if any_off else Qt.Unchecked
+        self._table.blockSignals(True)
+        for r in range(rows):
+            item = self._table.item(r, _COL_TRAIL)
+            if item:
+                key = item.data(Qt.UserRole)
+                if key:
+                    self._trail_enabled[key] = (new_state == Qt.Checked)
+                item.setCheckState(new_state)
+        self._table.blockSignals(False)
+        self._sky.update_data(self._visible_sats(), self._active_trails())
+
     # ── Table ─────────────────────────────────────────────────────────────────
 
     def _rebuild_table(self, sats: list):
         sorted_sats = sorted(sats, key=lambda x: (x[1].gnss_id, x[1].sv_id))
-        new_keys = [(rid, sat.gnss_id, sat.sv_id) for rid, sat in sorted_sats]
+        new_keys    = [(rid, sat.gnss_id, sat.sv_id) for rid, sat in sorted_sats]
 
         if new_keys == self._table_keys:
             # Only values changed — update in place, scroll position untouched
+            self._table.blockSignals(True)
             for row, (_, sat) in enumerate(sorted_sats):
                 self._table.item(row, 2).setText(f"{sat.elevation:.0f}")
                 self._table.item(row, 3).setText(f"{sat.azimuth:.0f}")
                 self._table.item(row, 4).setText(f"{sat.cno:.1f}")
                 self._table.item(row, 5).setText("✓" if sat.used_in_fix else "")
+            self._table.blockSignals(False)
             return
 
         # Satellite set changed — full rebuild
         self._table_keys = new_keys
+        self._table.blockSignals(True)
         vp = self._table.viewport()
         vp.setUpdatesEnabled(False)
         self._table.setSortingEnabled(False)
         self._table.setRowCount(len(sorted_sats))
 
         for row, (rid, sat) in enumerate(sorted_sats):
+            key       = (rid, sat.gnss_id, sat.sv_id)
             gnss_name = GNSS_NAMES.get(sat.gnss_id, f'SYS{sat.gnss_id}')
-            bg = QColor(GNSS_COLORS.get(sat.gnss_id, '#9E9E9E'))
+            bg        = QColor(GNSS_COLORS.get(sat.gnss_id, '#9E9E9E'))
             bg.setAlpha(55)
             brush = QBrush(bg)
 
@@ -222,5 +282,14 @@ class SkyTab(QWidget):
             self._table.setItem(row, 5, cell("✓" if sat.used_in_fix else ""))
             self._table.setItem(row, 6, cell(rid))
 
+            trail_item = QTableWidgetItem()
+            trail_item.setFlags(Qt.ItemIsUserCheckable | Qt.ItemIsEnabled)
+            trail_item.setCheckState(
+                Qt.Checked if self._trail_enabled.get(key, False) else Qt.Unchecked)
+            trail_item.setData(Qt.UserRole, key)
+            trail_item.setTextAlignment(Qt.AlignCenter)
+            self._table.setItem(row, _COL_TRAIL, trail_item)
+
         self._table.setSortingEnabled(True)
         vp.setUpdatesEnabled(True)
+        self._table.blockSignals(False)

gui/sky_widget.py

@@ -45,13 +45,13 @@ class SkyRenderThread(QThread):
         self._queue: Queue = Queue(maxsize=1)
         self._running      = True
 
-    def submit(self, sats: list, width: int, height: int):
+    def submit(self, sats: list, trails: dict, width: int, height: int):
         # Discard any pending (not yet rendered) frame so we always render latest
         try:
             self._queue.get_nowait()
         except Empty:
             pass
-        self._queue.put((list(sats), width, height))
+        self._queue.put((list(sats), trails, width, height))
 
     def stop(self):
         self._running = False
@@ -71,14 +71,14 @@ class SkyRenderThread(QThread):
                 continue
             if item is None:
                 break
-            sats, w, h = item
+            sats, trails, w, h = item
             if w > 0 and h > 0:
-                img = self._render(sats, w, h)
+                img = self._render(sats, trails, w, h)
                 self.frame_ready.emit(img)
 
     # ── Drawing (runs in render thread — QPainter on QImage is thread-safe) ──
 
-    def _render(self, sats: list, w: int, h: int) -> QImage:
+    def _render(self, sats: list, trails: dict, w: int, h: int) -> QImage:
         img = QImage(w, h, QImage.Format_RGB32)
 
         p   = QPainter(img)
@@ -89,6 +89,8 @@ class SkyRenderThread(QThread):
 
         self._draw_bg(p, w, h)
         self._draw_grid(p, cx, cy, max_r)
+        if trails:
+            self._draw_trails(p, cx, cy, max_r, trails)
         self._draw_satellites(p, cx, cy, max_r, sats)
         self._draw_legend(p, sats)
 
@@ -138,6 +140,27 @@ class SkyRenderThread(QThread):
         p.setPen(Qt.NoPen)
         p.drawEllipse(QPointF(cx, cy), 3, 3)
 
+    def _draw_trails(self, p: QPainter, cx, cy, max_r, trails: dict):
+        for (_, gnss_id, _), points in trails.items():
+            n = len(points)
+            if n < 2:
+                continue
+            base_color = _GNSS_QCOLORS.get(gnss_id, _C_LABEL)
+            r, g, b = base_color.red(), base_color.green(), base_color.blue()
+
+            # Subsample to at most 120 points so rendering stays fast
+            step = max(1, n // 120)
+            pts  = points[::step]
+            m    = len(pts)
+
+            for i in range(1, m):
+                # Alpha fades from 15 (oldest) to 200 (newest)
+                alpha = int(15 + 185 * i / m)
+                p.setPen(QPen(QColor(r, g, b, alpha), 1.5))
+                x1, y1 = _polar_xy(cx, cy, max_r, pts[i - 1][0], pts[i - 1][1])
+                x2, y2 = _polar_xy(cx, cy, max_r, pts[i][0],     pts[i][1])
+                p.drawLine(QPointF(x1, y1), QPointF(x2, y2))
+
     def _draw_satellites(self, p: QPainter, cx, cy, max_r, sats):
         f = QFont(); f.setPointSize(7)
         p.setFont(f)
@@ -188,8 +211,9 @@ class SkyPlotWidget(QWidget):
 
     def __init__(self):
         super().__init__()
-        self._sats:  list       = []
+        self._sats:   list  = []
-        self._image: QImage     = None
+        self._trails: dict  = {}
+        self._image:  QImage = None
 
         self.setMinimumSize(400, 400)
         self.setSizePolicy(QSizePolicy.Expanding, QSizePolicy.Expanding)
@@ -206,16 +230,17 @@ class SkyPlotWidget(QWidget):
 
     # ── Public API ────────────────────────────────────────────────────────────
 
-    def update_data(self, sats: list):
+    def update_data(self, sats: list, trails: dict = None):
-        self._sats = sats
+        self._sats   = sats
-        self._thread.submit(sats, self.width(), self.height())
+        self._trails = trails or {}
+        self._thread.submit(sats, self._trails, self.width(), self.height())
 
     # ── Qt events ─────────────────────────────────────────────────────────────
 
     def resizeEvent(self, event):
         super().resizeEvent(event)
         if self._sats:
-            self._thread.submit(self._sats, self.width(), self.height())
+            self._thread.submit(self._sats, self._trails, self.width(), self.height())
 
     def paintEvent(self, _event):
         p = QPainter(self)