Fix issue #21 and add aircraft position tracking indicators

- Fix Debian package upgrade issue by separating upgrade vs remove behavior in prerm script
- Add aircraft position tracking statistics in merger GetStatistics() method
- Update frontend to display position tracking indicators in both header and stats view
- Format Go code to maintain consistency

🤖 Generated with [Claude Code](https://claude.ai/code)

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

assets/static/index.html

@@ -53,6 +53,7 @@
             <!-- Summary stats -->
             <div class="stats-summary">
                 <span id="aircraft-count">0 aircraft</span>
+                <span id="position-summary">0 positioned</span>
                 <span id="sources-count">0 sources</span>
                 <span id="active-clients">1 viewer</span>
                 <span id="connection-status" class="connection-status disconnected">Connecting...</span>
@@ -208,6 +209,14 @@
                         <h3>Max Range</h3>
                         <div class="stat-value" id="max-range">0 km</div>
                     </div>
+                    <div class="stat-card">
+                        <h3>Aircraft with Position</h3>
+                        <div class="stat-value" id="aircraft-with-position">0</div>
+                    </div>
+                    <div class="stat-card">
+                        <h3>Aircraft without Position</h3>
+                        <div class="stat-value" id="aircraft-without-position">0</div>
+                    </div>
                 </div>
                 
                 <!-- Charts -->

assets/static/js/modules/ui-manager.js

@@ -244,6 +244,8 @@ export class UIManager {
         const activeViewersEl = document.getElementById('active-viewers');
         const maxRangeEl = document.getElementById('max-range');
         const messagesSecEl = document.getElementById('messages-sec');
+        const aircraftWithPositionEl = document.getElementById('aircraft-with-position');
+        const aircraftWithoutPositionEl = document.getElementById('aircraft-without-position');
         
         if (totalAircraftEl) totalAircraftEl.textContent = this.aircraftData.size;
         if (activeSourcesEl) {
@@ -253,6 +255,14 @@ export class UIManager {
             activeViewersEl.textContent = this.stats.active_clients || 1;
         }
         
+        // Update position tracking statistics from backend
+        if (aircraftWithPositionEl) {
+            aircraftWithPositionEl.textContent = this.stats.aircraft_with_position || 0;
+        }
+        if (aircraftWithoutPositionEl) {
+            aircraftWithoutPositionEl.textContent = this.stats.aircraft_without_position || 0;
+        }
+        
         // Calculate max range
         let maxDistance = 0;
         for (const aircraft of this.aircraftData.values()) {
@@ -270,10 +280,18 @@ export class UIManager {
 
     updateHeaderInfo() {
         const aircraftCountEl = document.getElementById('aircraft-count');
+        const positionSummaryEl = document.getElementById('position-summary');
         const sourcesCountEl = document.getElementById('sources-count');
         const activeClientsEl = document.getElementById('active-clients');
         
         if (aircraftCountEl) aircraftCountEl.textContent = `${this.aircraftData.size} aircraft`;
+        
+        // Update position summary in header
+        if (positionSummaryEl) {
+            const positioned = this.stats.aircraft_with_position || 0;
+            positionSummaryEl.textContent = `${positioned} positioned`;
+        }
+        
         if (sourcesCountEl) sourcesCountEl.textContent = `${this.sourcesData.size} sources`;
         
         // Update active clients count

debian/DEBIAN/prerm

@@ -2,8 +2,8 @@
 set -e
 
 case "$1" in
-    remove|upgrade|deconfigure)
+    remove|deconfigure)
-        # Stop and disable the service
+        # Stop and disable the service on removal
         if systemctl is-active --quiet skyview-adsb.service; then
             systemctl stop skyview-adsb.service
         fi
@@ -12,6 +12,13 @@ case "$1" in
             systemctl disable skyview-adsb.service
         fi
         ;;
+    upgrade)
+        # Only stop service during upgrade, preserve enabled state
+        if systemctl is-active --quiet skyview-adsb.service; then
+            systemctl stop skyview-adsb.service
+        fi
+        # Don't disable - postinst will restart if service was enabled
+        ;;
 esac
 
 exit 0

internal/merger/merger.go

@@ -795,10 +795,13 @@ func (m *Merger) GetSources() []*Source {
 //
 // The statistics include:
 //   - total_aircraft: Current number of tracked aircraft
+//   - aircraft_with_position: Number of aircraft with valid position data
+//   - aircraft_without_position: Number of aircraft without position data
 //   - total_messages: Sum of all messages processed
 //   - active_sources: Number of currently connected sources
 //   - aircraft_by_sources: Distribution of aircraft by number of tracking sources
 //
+// The position statistics help assess data quality and tracking effectiveness.
 // The aircraft_by_sources map shows data quality - aircraft tracked by
 // multiple sources generally have better position accuracy and reliability.
 //
@@ -810,11 +813,22 @@ func (m *Merger) GetStatistics() map[string]interface{} {
 	totalMessages := int64(0)
 	activeSources := 0
 	aircraftBySources := make(map[int]int) // Count by number of sources
+	aircraftWithPosition := 0
+	aircraftWithoutPosition := 0
 
 	for _, state := range m.aircraft {
 		totalMessages += state.TotalMessages
 		numSources := len(state.Sources)
 		aircraftBySources[numSources]++
+
+		// Check if aircraft has valid position data
+		if state.Aircraft.PositionValid &&
+			state.Aircraft.Latitude != 0.0 &&
+			state.Aircraft.Longitude != 0.0 {
+			aircraftWithPosition++
+		} else {
+			aircraftWithoutPosition++
+		}
 	}
 
 	for _, src := range m.sources {
@@ -824,10 +838,12 @@ func (m *Merger) GetStatistics() map[string]interface{} {
 	}
 
 	return map[string]interface{}{
-		"total_aircraft":      len(m.aircraft),
+		"total_aircraft":            len(m.aircraft),
-		"total_messages":      totalMessages,
+		"aircraft_with_position":    aircraftWithPosition,
-		"active_sources":      activeSources,
+		"aircraft_without_position": aircraftWithoutPosition,
-		"aircraft_by_sources": aircraftBySources,
+		"total_messages":            totalMessages,
+		"active_sources":            activeSources,
+		"aircraft_by_sources":       aircraftBySources,
 	}
 }
 

internal/modes/decoder.go

@@ -157,9 +157,9 @@ type Aircraft struct {
 	BaroSetting      float64 // Barometric pressure setting (QNH) in millibars
 
 	// Additional fields from VRS JSON and extended sources
-	Registration      string // Aircraft registration (e.g., "N12345")
+	Registration string // Aircraft registration (e.g., "N12345")
-	AircraftType      string // Aircraft type (e.g., "B738")
+	AircraftType string // Aircraft type (e.g., "B738")
-	Operator          string // Airline or operator name
+	Operator     string // Airline or operator name
 
 	// Validity flags for optional fields (used by VRS and other sources)
 	CallsignValid     bool // Whether callsign is valid

internal/vrs/parser.go

@@ -34,29 +34,29 @@ type VRSMessage struct {
 
 // VRSAircraft represents a single aircraft in VRS JSON format
 type VRSAircraft struct {
-	Icao  string  `json:"Icao"`  // ICAO hex address (may have ~ prefix for non-ICAO)
+	Icao string  `json:"Icao"` // ICAO hex address (may have ~ prefix for non-ICAO)
-	Lat   float64 `json:"Lat"`   // Latitude
+	Lat  float64 `json:"Lat"`  // Latitude
-	Long  float64 `json:"Long"`  // Longitude
+	Long float64 `json:"Long"` // Longitude
-	Alt   int     `json:"Alt"`   // Barometric altitude in feet
+	Alt  int     `json:"Alt"`  // Barometric altitude in feet
-	GAlt  int     `json:"GAlt"`  // Geometric altitude in feet
+	GAlt int     `json:"GAlt"` // Geometric altitude in feet
-	Spd   float64 `json:"Spd"`   // Speed in knots
+	Spd  float64 `json:"Spd"`  // Speed in knots
-	Trak  float64 `json:"Trak"`  // Track/heading in degrees
+	Trak float64 `json:"Trak"` // Track/heading in degrees
-	Vsi   int     `json:"Vsi"`   // Vertical speed in feet/min
+	Vsi  int     `json:"Vsi"`  // Vertical speed in feet/min
-	Sqk   string  `json:"Sqk"`   // Squawk code
+	Sqk  string  `json:"Sqk"`  // Squawk code
-	Call  string  `json:"Call"`  // Callsign
+	Call string  `json:"Call"` // Callsign
-	Gnd   bool    `json:"Gnd"`   // On ground flag
+	Gnd  bool    `json:"Gnd"`  // On ground flag
-	TAlt  int     `json:"TAlt"`  // Target altitude
+	TAlt int     `json:"TAlt"` // Target altitude
-	Mlat  bool    `json:"Mlat"`  // MLAT position flag
+	Mlat bool    `json:"Mlat"` // MLAT position flag
-	Tisb  bool    `json:"Tisb"`  // TIS-B flag
+	Tisb bool    `json:"Tisb"` // TIS-B flag
-	Sat   bool    `json:"Sat"`   // Satellite (JAERO) position flag
+	Sat  bool    `json:"Sat"`  // Satellite (JAERO) position flag
 
 	// Additional fields that may be present
-	Reg   string `json:"Reg"`   // Registration
+	Reg  string `json:"Reg"`  // Registration
-	Type  string `json:"Type"`  // Aircraft type
+	Type string `json:"Type"` // Aircraft type
-	Mdl   string `json:"Mdl"`   // Model
+	Mdl  string `json:"Mdl"`  // Model
-	Op    string `json:"Op"`    // Operator
+	Op   string `json:"Op"`   // Operator
-	From  string `json:"From"`  // Departure airport
+	From string `json:"From"` // Departure airport
-	To    string `json:"To"`    // Destination airport
+	To   string `json:"To"`   // Destination airport
 
 	// Timing fields
 	PosTime int64 `json:"PosTime"` // Position timestamp (milliseconds)