ekf2: block process noise increment without constraining the variance

The wind variance can be reset to a value larger than the wind init
variance (e.g.: when the reset occurs when flying close to the N or E
axis). Constraining the variance after a covariance initialization would
artificially increase the correlation and could destabilize the filter.

src/modules/ekf2/EKF/covariance.cpp

@@ -201,14 +201,15 @@ void Ekf::predictCovariance(const imuSample &imu_delayed)
 #if defined(CONFIG_EKF2_WIND)
 
 	// wind vel: add process noise
-	if (!_external_wind_init) {
-		float wind_vel_nsd_scaled = math::constrain(_params.wind_vel_nsd, 0.f, 1.f)
-					    * (1.f + _params.wind_vel_nsd_scaler * fabsf(_height_rate_lpf));
-		float wind_vel_process_noise = sq(wind_vel_nsd_scaled) * dt;
-
-		for (unsigned index = 0; index < State::wind_vel.dof; index++) {
-			const unsigned i = State::wind_vel.idx + index;
-			P(i, i) = fminf(P(i, i) + wind_vel_process_noise, sq(_params.initial_wind_uncertainty));
+	float wind_vel_nsd_scaled = math::constrain(_params.wind_vel_nsd, 0.f, 1.f)
+				    * (1.f + _params.wind_vel_nsd_scaler * fabsf(_height_rate_lpf));
+	float wind_vel_process_noise = sq(wind_vel_nsd_scaled) * dt;
+
+	for (unsigned index = 0; index < State::wind_vel.dof; index++) {
+		const unsigned i = State::wind_vel.idx + index;
+
+		if (P(i, i) < sq(_params.initial_wind_uncertainty)) {
+			P(i, i) += wind_vel_process_noise;
 		}
 	}