Added GPS DOP support (#199)

src/gps/GPS.cpp

@@ -68,6 +68,19 @@ void perhapsSetRTC(struct tm &t)
         perhapsSetRTC(&tv);
 }
 
+// Generate a string representation of the DOP
+//   based on Wikipedia "meaning of DOP values" https://en.wikipedia.org/wiki/Dilution_of_precision_(navigation)#Meaning_of_DOP_Values
+const char *getDOPString(uint32_t dop) {
+    dop = dop / 100;
+    if(dop <= 1) return "GPS Ideal";
+    if(dop <= 2) return "GPS Exc.";
+    if(dop <= 5) return "GPS Good";
+    if(dop <= 10) return "GPS Mod.";
+    if(dop <= 20) return "GPS Fair";
+    if(dop > 0) return "GPS Poor";
+    return "invalid dop";
+}
+
 #include <time.h>
 
 uint32_t getTime()

src/gps/GPS.h

@@ -8,6 +8,9 @@
 void perhapsSetRTC(const struct timeval *tv);
 void perhapsSetRTC(struct tm &t);
 
+// Generate a string representation of DOP
+const char *getDOPString(uint32_t dop);
+
 /// Return time since 1970 in secs.  Until we have a GPS lock we will be returning time based at zero
 uint32_t getTime();
 
@@ -31,6 +34,8 @@ class GPS : public Observable<void *>
   public:
     int32_t latitude = 0, longitude = 0; // as an int mult by 1e-7 to get value as double
     int32_t altitude = 0;
+    uint32_t dop = 0; // Diminution of position; PDOP where possible (UBlox), HDOP otherwise (TinyGPS) in 10^2 units (needs scaling before use)
+
     bool isConnected = false; // Do we have a GPS we are talking to
 
     virtual ~GPS() {}

src/gps/NEMAGPS.cpp

@@ -53,9 +53,13 @@ void NEMAGPS::loop()
                 latitude = toDegInt(loc.lat);
                 longitude = toDegInt(loc.lng);
             }
+            // Diminution of precision (an accuracy metric) is reported in 10^2 units, so we need to scale down when we use it
+            if(reader.hdop.isValid()) {
+                dop = reader.hdop.value();
+            }
 
             // expect gps pos lat=37.520825, lon=-122.309162, alt=158
-            DEBUG_MSG("new NEMA GPS pos lat=%f, lon=%f, alt=%d\n", latitude * 1e-7, longitude * 1e-7, altitude);
+            DEBUG_MSG("new NEMA GPS pos lat=%f, lon=%f, alt=%d, hdop=%f\n", latitude * 1e-7, longitude * 1e-7, altitude, dop * 1e-2);
 
             hasValidLocation = (latitude != 0) || (longitude != 0); // bogus lat lon is reported as 0,0
             if (hasValidLocation)

src/gps/UBloxGPS.cpp

@@ -115,7 +115,8 @@ The Unix epoch (or Unix time or POSIX time or Unix timestamp) is the number of s
         latitude = ublox.getLatitude();
         longitude = ublox.getLongitude();
         altitude = ublox.getAltitude() / 1000; // in mm convert to meters
-        DEBUG_MSG("new gps pos lat=%f, lon=%f, alt=%d\n", latitude * 1e-7, longitude * 1e-7, altitude);
+        dop = ublox.getPDOP(); // PDOP (an accuracy metric) is reported in 10^2 units so we have to scale down when we use it
+        DEBUG_MSG("new gps pos lat=%f, lon=%f, alt=%d, pdop=%f\n", latitude * 1e-7, longitude * 1e-7, altitude, dop * 1e-2);
 
         // bogus lat lon is reported as 0 or 0 (can be bogus just for one)
         // Also: apparently when the GPS is initially reporting lock it can output a bogus latitude > 90 deg!

src/main.cpp

@@ -334,8 +334,7 @@ void loop()
     screen.debug()->setNodeNumbersStatus(nodeDB.getNumOnlineNodes(), nodeDB.getNumNodes());
     screen.debug()->setChannelNameStatus(channelSettings.name);
     screen.debug()->setPowerStatus(powerStatus);
-    // TODO(#4): use something based on hdop to show GPS "signal" strength.
-    screen.debug()->setGPSStatus(gps->isConnected ? (gps->hasLock() ? "GPS ok" : "No Sats") : "No GPS");
+    screen.debug()->setGPSStatus(gps->isConnected ? (gps->hasLock() ? getDOPString(gps->dop) : "No Sats") : "No GPS");
 
     // No GPS lock yet, let the OS put the main CPU in low power mode for 100ms (or until another interrupt comes in)
     // i.e. don't just keep spinning in loop as fast as we can.