Adding ambiguity to APRS message

APRSPacketLib.patch

diff --git a/include/APRSPacketLib.h b/include/APRSPacketLib.h
index aed7772..9171477 100644
--- a/include/APRSPacketLib.h
+++ b/include/APRSPacketLib.h
@@ -45,10 +45,10 @@ namespace APRSPacketLib {
 
     String  generateDigipeatedPacket(const String& packet, const String &callsign, const String& path);
 
-    String  encodeGPSIntoBase91(float latitude, float longitude, float course, float speed, const String& symbol, bool sendAltitude = false, int altitude = 0, bool sendStandingUpdate = false);
+    String  encodeGPSIntoBase91(float latitude, float longitude, float course, float speed, const String& symbol, bool sendAltitude = false, int altitude = 0, bool sendStandingUpdate = false, int ambiguity_level = 2);
     String  generateBase91GPSBeaconPacket(const String& callsign, const String& tocall, const String& path, const String& overlay, const String& gpsData);
 
-    String  generateMiceGPSBeaconPacket(const String& miceMsgType, const String& callsign, const String& symbol, const String& overlay, const String& path, float latitude, float longitude, float course, float speed, int altitude);
+    String  generateMiceGPSBeaconPacket(const String& miceMsgType, const String& callsign, const String& symbol, const String& overlay, const String& path, float latitude, float longitude, float course, float speed, int altitude, int ambiguity_level = 2);
 
     APRSPacket processReceivedPacket(const String& receivedPacket, int rssi, float snr, int freqError);
 
diff --git a/src/APRSPacketLib.cpp b/src/APRSPacketLib.cpp
index 48daa1c..3ff008b 100644
--- a/src/APRSPacketLib.cpp
+++ b/src/APRSPacketLib.cpp
@@ -28,9 +28,46 @@ _______________________________________________*/
 
 
 #include <APRSPacketLib.h>
+#include <cmath>
 
 namespace APRSPacketLib {
 
+    /**
+     * @brief Applies ambiguity to a GPS coordinate by reducing its precision.
+     *
+     * This function implements the standard APRS position ambiguity by truncating
+     * the decimal part of the coordinate's minutes. The new, less-precise
+     * coordinate is then used for encoding.
+     *
+     * @param coordinate The original coordinate in decimal degrees.
+     * @param ambiguity_level An integer from 0 to 4.
+     *        - 0: No ambiguity.
+     *        - 1: Reduces precision to 0.1 minutes (e.g., 4903.5_N).
+     *        - 2: Reduces precision to 1 minute (e.g., 4903.__N).
+     *        - 3: Reduces precision to 10 minutes (e.g., 490_.__N).
+     *        - 4: Reduces precision to 1 degree (e.g., 49__.__N).
+     * @return The coordinate with reduced precision.
+     */
+    float apply_ambiguity(float coordinate, int ambiguity_level) {
+        if (ambiguity_level <= 0) {
+            return coordinate;
+        }
+
+        float deg = floorf(fabsf(coordinate));
+        float dec_minutes = (fabsf(coordinate) - deg) * 60.0f;
+
+        switch (ambiguity_level) {
+            case 1: dec_minutes = floorf(dec_minutes * 10.0f) / 10.0f; break;
+            case 2: dec_minutes = floorf(dec_minutes); break;
+            case 3: dec_minutes = floorf(dec_minutes / 10.0f) * 10.0f; break;
+            default: dec_minutes = 0.0f; break; // Level 4 and higher
+        }
+
+        float new_coordinate = deg + dec_minutes / 60.0f;
+
+        return copysignf(new_coordinate, coordinate);
+    }
+
     String generateBasePacket(const String& callsign, const String& tocall, const String& path) {
         String packet = callsign;
         packet += ">";
@@ -91,7 +128,14 @@ namespace APRSPacketLib {
         return(s);
     }
 
-    String encodeGPSIntoBase91(float latitude, float longitude, float course, float speed, const String& symbol, bool sendAltitude, int altitude, bool sendStandingUpdate) {
+    String encodeGPSIntoBase91(float latitude, float longitude, float course, float speed, const String& symbol, bool sendAltitude, int altitude, bool sendStandingUpdate, int ambiguity_level) {
+        // Apply ambiguity to the coordinates if requested.
+        // This truncates the precision before encoding.
+        if (ambiguity_level > 0) {
+            latitude = apply_ambiguity(latitude, ambiguity_level);
+            longitude = apply_ambiguity(longitude, ambiguity_level);
+        }
+
         String encodedData;
         uint32_t aprs_lat, aprs_lon;
         aprs_lat = 900000000 - latitude * 10000000;
@@ -386,7 +430,7 @@ namespace APRSPacketLib {
         buf[2] = h28;
     }
 
-    void encodeMiceDestinationField(const String& msgType, uint8_t *buf, const gpsLatitudeStruct *lat, const gpsLongitudeStruct *lon) {
+    void encodeMiceDestinationField(const String& msgType, uint8_t *buf, const gpsLatitudeStruct *lat, const gpsLongitudeStruct *lon, int ambiguity_level) {
         uint32_t temp;
         temp = lat->degrees / 10;             // degrees
         buf[0] = (temp + 0x30);
@@ -402,6 +446,18 @@ namespace APRSPacketLib {
         temp   = lat->minuteHundredths/10;  // minute hundredths
         buf[4] = (temp + 0x30) + ((lon->degrees >= 100 || lon->degrees <= 9) ? 0x20 : 0);   // Longitude Offset
         buf[5] = (lat->minuteHundredths - temp * 10 + 0x30) + (!lon->east ? 0x20 : 0);      // West validation
+
+        // Per APRS spec, ambiguity in Mic-E is shown by replacing characters with spaces.
+        // This is done *after* encoding the (already truncated) coordinate value.
+        if (ambiguity_level >= 1) {
+            buf[5] = ' '; // Obscure 1/100th of a minute
+        }
+        if (ambiguity_level >= 2) {
+            buf[4] = ' '; // Obscure 1/10th of a minute
+        }
+        if (ambiguity_level >= 3) {
+            buf[3] = ' '; // Obscure 1 minute
+        }
     }
 
     String doubleToString(double n, int ndec) {
@@ -494,12 +550,18 @@ namespace APRSPacketLib {
         return miceLongitudeStruct;
     }
 
-    String generateMiceGPSBeaconPacket(const String& miceMsgType, const String& callsign, const String& symbol, const String& overlay, const String& path, float latitude, float longitude, float course, float speed, int altitude) {
+    String generateMiceGPSBeaconPacket(const String& miceMsgType, const String& callsign, const String& symbol, const String& overlay, const String& path, float latitude, float longitude, float course, float speed, int altitude, int ambiguity_level) {
+        // Apply ambiguity to the coordinates if requested. This truncates the precision.
+        if (ambiguity_level > 0) {
+            latitude = apply_ambiguity(latitude, ambiguity_level);
+            longitude = apply_ambiguity(longitude, ambiguity_level);
+        }
+
         gpsLatitudeStruct latitudeStruct    = gpsDecimalToDegreesMiceLatitude(latitude);
         gpsLongitudeStruct longitudeStruct  = gpsDecimalToDegreesMiceLongitude(longitude);
 
         uint8_t miceDestinationArray[7];
-        encodeMiceDestinationField(miceMsgType, &miceDestinationArray[0], &latitudeStruct, &longitudeStruct);
+        encodeMiceDestinationField(miceMsgType, &miceDestinationArray[0], &latitudeStruct, &longitudeStruct, ambiguity_level);
         miceDestinationArray[6] = 0x00;     // por repetidor?
         String miceDestination = (char*)miceDestinationArray;
 
diff --git a/src/keyboard_utils.cpp b/src/keyboard_utils.cpp
index bd7b22c..a0ed6ad 100644
--- a/src/keyboard_utils.cpp
+++ b/src/keyboard_utils.cpp
@@ -746,7 +746,7 @@ namespace KEYBOARD_Utils {
             } else if (key == 13 && messageText.length() > 0) {
                 messageText.trim();
                 if (messageText.length() > 67) messageText = messageText.substring(0, 67);
-                String packet = APRSPacketLib::generateBase91GPSBeaconPacket(currentBeacon->callsign, "APLRT1", Config.path, currentBeacon->overlay, APRSPacketLib::encodeGPSIntoBase91(gps.location.lat(),gps.location.lng(), gps.course.deg(), gps.speed.knots(), currentBeacon->symbol, Config.sendAltitude, gps.altitude.feet(), sendStandingUpdate));
+                String packet = APRSPacketLib::generateBase91GPSBeaconPacket(currentBeacon->callsign, "APLRT1", Config.path, currentBeacon->overlay, APRSPacketLib::encodeGPSIntoBase91(gps.location.lat(),gps.location.lng(), gps.course.deg(), gps.speed.knots(), currentBeacon->symbol, Config.sendAltitude, gps.altitude.feet(), sendStandingUpdate, 2));
                 packet += messageText;
                 displayShow("<<< TX >>>", "", packet,100);
                 LoRa_Utils::sendNewPacket(packet);       
diff --git a/src/station_utils.cpp b/src/station_utils.cpp
index 07f7b87..10eb694 100644
--- a/src/station_utils.cpp
+++ b/src/station_utils.cpp
@@ -198,9 +198,9 @@ namespace STATION_Utils {
         if (gps.speed.kmph() > 200 || gps.altitude.meters() > 9000) path = ""; // avoid plane speed and altitude
         String packet;
         if (miceActive) {
-            packet = APRSPacketLib::generateMiceGPSBeaconPacket(currentBeacon->micE, currentBeacon->callsign, currentBeacon->symbol, currentBeacon->overlay, path, gps.location.lat(), gps.location.lng(), gps.course.deg(), gps.speed.knots(), gps.altitude.meters());
+            packet = APRSPacketLib::generateMiceGPSBeaconPacket(currentBeacon->micE, currentBeacon->callsign, currentBeacon->symbol, currentBeacon->overlay, path, gps.location.lat(), gps.location.lng(), gps.course.deg(), gps.speed.knots(), gps.altitude.meters(), 2);
         } else {
-            packet = APRSPacketLib::generateBase91GPSBeaconPacket(currentBeacon->callsign, "APLRT1", path, currentBeacon->overlay, APRSPacketLib::encodeGPSIntoBase91(gps.location.lat(),gps.location.lng(), gps.course.deg(), gps.speed.knots(), currentBeacon->symbol, Config.sendAltitude, gps.altitude.feet(), sendStandingUpdate));
+            packet = APRSPacketLib::generateBase91GPSBeaconPacket(currentBeacon->callsign, "APLRT1", path, currentBeacon->overlay, APRSPacketLib::encodeGPSIntoBase91(gps.location.lat(),gps.location.lng(), gps.course.deg(), gps.speed.knots(), currentBeacon->symbol, Config.sendAltitude, gps.altitude.feet(), sendStandingUpdate, 2));
         }
 
         String batteryVoltage = BATTERY_Utils::getBatteryInfoVoltage();