Airspeed measurement: Add accurate models for dynamic pressure

This allows to get very accurate readings from the SDP3x sensor series from Sensirion using a complete sensor model.

src/modules/sensors/parameters.cpp

@@ -157,6 +157,10 @@ int initialize_parameter_handles(ParameterHandles &parameter_handles)
 
 	parameter_handles.vibe_thresh = param_find("ATT_VIBE_THRESH");
 
+	parameter_handles.air_pmodel = param_find("CAL_AIR_PMODEL");
+	parameter_handles.air_smodel = param_find("CAL_AIR_SMODEL");
+	parameter_handles.air_tube_length = param_find("CAL_AIR_TUBELEN");
+
 	// These are parameters for which QGroundControl always expects to be returned in a list request.
 	// We do a param_find here to force them into the list.
 	(void)param_find("RC_CHAN_CNT");
@@ -488,6 +492,10 @@ int update_parameters(const ParameterHandles &parameter_handles, Parameters &par
 
 	param_get(parameter_handles.vibe_thresh, &parameters.vibration_warning_threshold);
 
+	param_get(parameter_handles.air_pmodel, &parameters.air_pmodel);
+	param_get(parameter_handles.air_smodel, &parameters.air_smodel);
+	param_get(parameter_handles.air_tube_length, &parameters.air_tube_length);
+
 	return ret;
 }
 

src/modules/sensors/parameters.h

@@ -146,6 +146,10 @@ struct Parameters {
 
 	float vibration_warning_threshold;
 
+	int32_t air_pmodel;
+	int32_t air_smodel;
+	float air_tube_length;
+
 };
 
 struct ParameterHandles {
@@ -227,6 +231,10 @@ struct ParameterHandles {
 
 	param_t vibe_thresh; /**< vibration threshold */
 
+	param_t air_pmodel;
+	param_t air_smodel;
+	param_t air_tube_length;
+
 };
 
 /**

src/modules/sensors/sensor_params.c

@@ -1,6 +1,6 @@
 /****************************************************************************
  *
- *   Copyright (c) 2012-2016 PX4 Development Team. All rights reserved.
+ *   Copyright (c) 2012-2017 PX4 Development Team. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -814,6 +814,35 @@ PARAM_DEFINE_INT32(CAL_MAG_SIDES, 63);
  */
 PARAM_DEFINE_INT32(CAL_BARO_PRIME, 0);
 
+/**
+ * Airspeed sensor pitot model
+ *
+ * @value 0 HB Pitot
+ *
+ * @group Sensor Calibration
+ */
+PARAM_DEFINE_INT32(CAL_AIR_PMODEL, 0);
+
+/**
+ * Airspeed sensor model
+ *
+ * @value 0 Membrane sensor
+ * @value 1 Sensirion SDP3x
+ *
+ * @group Sensor Calibration
+ */
+PARAM_DEFINE_INT32(CAL_AIR_SMODEL, 0);
+
+/**
+ * Airspeed sensor tube length
+ * @min 0.01
+ * @max 0.5
+ * @unit meter
+ *
+ * @group Sensor Calibration
+ */
+PARAM_DEFINE_FLOAT(CAL_AIR_TUBELEN, 0.15);
+
 /**
  * Differential pressure sensor offset
  *

src/modules/sensors/sensors.cpp

@@ -326,10 +326,13 @@ Sensors::diff_pres_poll(struct sensor_combined_s &raw)
 
 		/* don't risk to feed negative airspeed into the system */
 		_airspeed.indicated_airspeed_m_s = math::max(0.0f,
-						   calc_indicated_airspeed(_diff_pres.differential_pressure_filtered_pa));
+						   calc_indicated_airspeed_corrected((enum AIRSPEED_PITOT_MODEL)_parameters.air_pmodel,
+								   (enum AIRSPEED_SENSOR_MODEL)_parameters.air_smodel, _parameters.air_tube_length,
+								   _diff_pres.differential_pressure_filtered_pa, _voted_sensors_update.baro_pressure(),
+								   air_temperature_celsius));
 
 		_airspeed.true_airspeed_m_s = math::max(0.0f,
-							calc_true_airspeed(_diff_pres.differential_pressure_filtered_pa + _voted_sensors_update.baro_pressure(),
+							calc_true_airspeed_from_indicated(_airspeed.indicated_airspeed_m_s,
 									_voted_sensors_update.baro_pressure(), air_temperature_celsius));
 
 		_airspeed.true_airspeed_unfiltered_m_s = math::max(0.0f,