fix diff

Solutions/Inc/Nmea_Gga.h

@@ -13,6 +13,7 @@
 #define DGPS_SID_MIN   (0000)
 #define DGPS_SID_MAX   (1023)
 
+#define DIFF_GEOID_IS_BELOW '-'
 /**
  * GPS Quality indicator:
  */

Solutions/Src/Nmea_Gga.c

@@ -53,7 +53,9 @@ bool NmeaGga_Parse(char *str, size_t len, tNmeaGGA *result)
             *front : 0;
     result->diff =
             (Nmea0183ParseNextPortion(&front, &nextDivider, end) > 0) ?
-            Nmea0183ParseDouble(front,nextDivider - front) : 0;
+            (*front != DIFF_GEOID_IS_BELOW) ?
+            Nmea0183ParseDouble(front,nextDivider - front) : 0
+            : 0;
     result->diff_units =
             (Nmea0183ParseNextPortion(&front, &nextDivider, end) > 0) ?
             *front : 0;