AP_GPS: prevent use of blended GPS with moving baseline

when moving baseline is enabled the rover is slaved to the base for
position and velocity, adding no additional useful data. Only the yaw
comes from the rover

libraries/AP_GPS/AP_GPS.cpp

@@ -1149,8 +1149,18 @@ void AP_GPS::update(void)
 void AP_GPS::update_primary(void)
 {
 #if defined(GPS_BLENDED_INSTANCE)
-    // if blending is requested, attempt to calculate weighting for each GPS
-    if ((GPSAutoSwitch)_auto_switch.get() == GPSAutoSwitch::BLEND) {
+    /*
+      if blending is requested, attempt to calculate weighting for
+      each GPS
+      we do not do blending if using moving baseline yaw as the rover is
+      significant lagged and gives no more information on position or
+      velocity
+    */
+    const bool using_moving_base = (_type[0] == GPS_TYPE_UAVCAN_RTK_BASE ||
+                                    _type[0] == GPS_TYPE_UBLOX_RTK_BASE ||
+                                    _type[1] == GPS_TYPE_UAVCAN_RTK_BASE ||
+                                    _type[1] == GPS_TYPE_UBLOX_RTK_BASE);
+    if ((GPSAutoSwitch)_auto_switch.get() == GPSAutoSwitch::BLEND && !using_moving_base) {
         _output_is_blended = calc_blend_weights();
         // adjust blend health counter
         if (!_output_is_blended) {