position_estimator_inav: GPS delay compensation

src/modules/position_estimator_inav/position_estimator_inav_main.c

@@ -71,6 +71,8 @@
 #include "inertial_filter.h"
 
 #define MIN_VALID_W 0.00001f
+#define PUB_INTERVAL 10000	// limit publish rate to 100 Hz
+#define EST_BUF_SIZE 500000 / PUB_INTERVAL		// buffer size is 0.5s
 
 static bool thread_should_exit = false; /**< Deamon exit flag */
 static bool thread_running = false; /**< Deamon status flag */
@@ -83,7 +85,6 @@ static const hrt_abstime sonar_timeout = 150000;	// sonar timeout = 150ms
 static const hrt_abstime sonar_valid_timeout = 1000000;	// estimate sonar distance during this time after sonar loss
 static const hrt_abstime xy_src_timeout = 2000000;	// estimate position during this time after position sources loss
 static const uint32_t updates_counter_len = 1000000;
-static const uint32_t pub_interval = 10000;	// limit publish rate to 100 Hz
 static const float max_flow = 1.0f;	// max flow value that can be used, rad/s
 
 __EXPORT int position_estimator_inav_main(int argc, char *argv[]);
@@ -92,6 +93,16 @@ int position_estimator_inav_thread_main(int argc, char *argv[]);
 
 static void usage(const char *reason);
 
+static inline int min(int val1, int val2)
+{
+	return (val1 < val2) ? val1 : val2;
+}
+
+static inline int max(int val1, int val2)
+{
+	return (val1 > val2) ? val1 : val2;
+}
+
 /**
  * Print the correct usage.
  */
@@ -199,6 +210,10 @@ int position_estimator_inav_thread_main(int argc, char *argv[])
 	float y_est[2] = { 0.0f, 0.0f };	// pos, vel
 	float z_est[2] = { 0.0f, 0.0f };	// pos, vel
 
+	float est_buf[EST_BUF_SIZE][3][2];
+	memset(est_buf, 0, sizeof(est_buf));
+	int est_buf_ptr = 0;
+
 	float eph = 1.0;
 	float epv = 1.0;
 
@@ -657,16 +672,22 @@ int position_estimator_inav_thread_main(int argc, char *argv[])
 							y_est[1] = gps.vel_e_m_s;
 						}
 
+						/* calculate index of estimated values in buffer */
+						int est_i = est_buf_ptr - 1 - min(EST_BUF_SIZE - 1, max(0, (int)(params.delay_gps * 1000000.0f / PUB_INTERVAL)));
+						if (est_i < 0) {
+							est_i += EST_BUF_SIZE;
+						}
+
 						/* calculate correction for position */
-						corr_gps[0][0] = gps_proj[0] - x_est[0];
+						corr_gps[0][0] = gps_proj[0] - est_buf[est_i][0][0];
-						corr_gps[1][0] = gps_proj[1] - y_est[0];
+						corr_gps[1][0] = gps_proj[1] - est_buf[est_i][1][0];
-						corr_gps[2][0] = local_pos.ref_alt - alt - z_est[0];
+						corr_gps[2][0] = local_pos.ref_alt - alt - est_buf[est_i][2][0];
 
 						/* calculate correction for velocity */
 						if (gps.vel_ned_valid) {
-							corr_gps[0][1] = gps.vel_n_m_s - x_est[1];
+							corr_gps[0][1] = gps.vel_n_m_s - est_buf[est_i][0][1];
-							corr_gps[1][1] = gps.vel_e_m_s - y_est[1];
+							corr_gps[1][1] = gps.vel_e_m_s - est_buf[est_i][1][1];
-							corr_gps[2][1] = gps.vel_d_m_s - z_est[1];
+							corr_gps[2][1] = gps.vel_d_m_s - est_buf[est_i][2][1];
 
 						} else {
 							corr_gps[0][1] = 0.0f;
@@ -910,8 +931,21 @@ int position_estimator_inav_thread_main(int argc, char *argv[])
 			}
 		}
 
-		if (t > pub_last + pub_interval) {
+		if (t > pub_last + PUB_INTERVAL) {
 			pub_last = t;
+
+			/* push current estimate to FIFO buffer */
+			est_buf[est_buf_ptr][0][0] = x_est[0];
+			est_buf[est_buf_ptr][0][1] = x_est[1];
+			est_buf[est_buf_ptr][1][0] = y_est[0];
+			est_buf[est_buf_ptr][1][1] = y_est[1];
+			est_buf[est_buf_ptr][2][0] = z_est[0];
+			est_buf[est_buf_ptr][2][1] = z_est[1];
+			est_buf_ptr++;
+			if (est_buf_ptr >= EST_BUF_SIZE) {
+				est_buf_ptr = 0;
+			}
+
 			/* publish local position */
 			local_pos.xy_valid = can_estimate_xy;
 			local_pos.v_xy_valid = can_estimate_xy;

src/modules/position_estimator_inav/position_estimator_inav_params.c

@@ -55,6 +55,7 @@ PARAM_DEFINE_FLOAT(INAV_SONAR_ERR, 0.5f);
 PARAM_DEFINE_FLOAT(INAV_LAND_T, 3.0f);
 PARAM_DEFINE_FLOAT(INAV_LAND_DISP, 0.7f);
 PARAM_DEFINE_FLOAT(INAV_LAND_THR, 0.2f);
+PARAM_DEFINE_FLOAT(INAV_DELAY_GPS, 0.1f);
 
 int parameters_init(struct position_estimator_inav_param_handles *h)
 {
@@ -73,6 +74,7 @@ int parameters_init(struct position_estimator_inav_param_handles *h)
 	h->land_t = param_find("INAV_LAND_T");
 	h->land_disp = param_find("INAV_LAND_DISP");
 	h->land_thr = param_find("INAV_LAND_THR");
+	h->delay_gps = param_find("INAV_DELAY_GPS");
 
 	return OK;
 }
@@ -94,6 +96,7 @@ int parameters_update(const struct position_estimator_inav_param_handles *h, str
 	param_get(h->land_t, &(p->land_t));
 	param_get(h->land_disp, &(p->land_disp));
 	param_get(h->land_thr, &(p->land_thr));
+	param_get(h->delay_gps, &(p->delay_gps));
 
 	return OK;
 }

src/modules/position_estimator_inav/position_estimator_inav_params.h

@@ -56,6 +56,7 @@ struct position_estimator_inav_params {
 	float land_t;
 	float land_disp;
 	float land_thr;
+	float delay_gps;
 };
 
 struct position_estimator_inav_param_handles {
@@ -74,6 +75,7 @@ struct position_estimator_inav_param_handles {
 	param_t land_t;
 	param_t land_disp;
 	param_t land_thr;
+	param_t delay_gps;
 };
 
 /**