AP_Baro Detailed Reference¶

AP_Baro is the core barometer (air pressure) sensor driver for ArduPilot. It provides altitude estimation based on atmospheric pressure readings, which is critical for maintaining altitude in fixed-wing aircraft and for altitude hold in multirotors.

Key Features:

Multiple barometer backend support (BMP280, MS5611, BMP388, etc.)
Altitude calculation using barometric formula
Pressure correction for temperature and wind effects
Ground pressure/temperature tracking
EAS (Equivalent Airspeed) to TAS (True Airspeed) conversion
Sensor fusion with GPS for improved accuracy

Inheritance ¶

This class does not inherit from any other class. It is a top-level driver class.

Derived Classes:

:doxygen:`AP_Baro_BMP280` - Bosch BMP280 barometer
:doxygen:`AP_Baro_MS5611` - Measurement Specialties MS5611 barometer
:doxygen:`AP_Baro_BMP388` - Bosch BMP388 barometer
:doxygen:`AP_Baro_BMP581` - Bosch BMP581 barometer

Related Classes:

:doxygen:`AP_Baro_Backend` - Base class for barometer backends

Public Types ¶

enum AP_Baro::baro_type_t¶

Barometer type/sensor model.

Noindex:

BARO_TYPE_AIRPRESSURE = 0,  // Standard air pressure sensor
BARO_TYPE_WIND = 1,          // Wind pressure sensor
BARO_TYPE_WIND_TUNNEL = 2   // Wind tunnel pressure sensor

Public Member Variables ¶

AP_Baro::sensor sensors[BARO_MAX_INSTANCES]¶: Array of barometer sensor data structures containing pressure, temperature, altitude, etc.

Public Member Functions ¶

Singleton ¶

static AP_Baro *AP_Baro::get_singleton(void)¶

Get singleton instance of the barometer driver.

Returns:: Pointer to AP_Baro instance, or nullptr if not available

AP_Baro *baro = AP_Baro::get_singleton();
if (baro == nullptr) {
    // Baro not available
}

Initialization & Update ¶

void AP_Baro::update(void)¶: Update barometer readings. Must be called in main loop.

void AP_Baro::calibrate(bool save = true)¶

Calibrate barometer. Saves calibration if save is true.

Parameters:: save – Whether to save calibration to persistent storage

void AP_Baro::update_calibration(void)¶: Update running calibration parameters.

Health & Status ¶

bool AP_Baro::healthy(void) const¶

Check if primary barometer is healthy.

Returns:: true if barometer is healthy

bool AP_Baro::healthy(uint8_t instance) const¶

Check if specific barometer instance is healthy.

Parameters:: instance – Barometer instance index
Returns:: true if healthy

bool AP_Baro::all_healthy(void) const¶

Check if all barometers are healthy.

Returns:: true if all barometers are healthy

uint8_t AP_Baro::get_primary(void) const¶

Get primary barometer instance.

Returns:: Primary barometer instance index

Pressure Data ¶

float AP_Baro::get_pressure(void) const¶

Get current pressure from primary barometer.

Returns:: Pressure in Pa

float AP_Baro::get_pressure(uint8_t instance) const¶

Get pressure from specific barometer instance.

Parameters:: instance – Barometer instance index
Returns:: Pressure in Pa

const Vector3f &AP_Baro::get_dynamic_pressure(uint8_t instance) const¶

Get dynamic pressure vector (for airspeed calculation).

Parameters:: instance – Barometer instance index
Returns:: Vector3f with dynamic pressure

float AP_Baro::get_corrected_pressure(uint8_t instance) const¶

Get corrected pressure (with wind/temperature corrections).

Parameters:: instance – Barometer instance index
Returns:: Corrected pressure in Pa

Temperature Data ¶

float AP_Baro::get_temperature(void) const¶

Get temperature from primary barometer.

Returns:: Temperature in Celsius

float AP_Baro::get_temperature(uint8_t instance) const¶

Get temperature from specific barometer instance.

Parameters:: instance – Barometer instance index
Returns:: Temperature in Celsius

Altitude Data ¶

float AP_Baro::get_altitude(void) const¶

Get altitude estimate from primary barometer.

Returns:: Altitude in meters (relative to ground)

float AP_Baro::get_altitude(uint8_t instance) const¶

Get altitude from specific barometer instance.

Parameters:: instance – Barometer instance index
Returns:: Altitude in meters

float AP_Baro::get_altitude_AMSL(uint8_t instance) const¶

Get altitude above mean sea level (AMSL).

Parameters:: instance – Barometer instance index
Returns:: Altitude in meters AMSL

float AP_Baro::get_altitude_AMSL(void) const¶

Get AMSL altitude from primary barometer.

Returns:: Altitude in meters AMSL

Climb Rate ¶

float AP_Baro::get_climb_rate(void)¶

Get estimated climb rate.

Returns:: Climb rate in m/s

Ground Reference ¶

float AP_Baro::get_ground_pressure(void) const¶

Get ground pressure (set during calibration).

Returns:: Ground pressure in Pa

float AP_Baro::get_ground_temperature(void) const¶

Get ground temperature (for altitude calculations).

Returns:: Ground temperature in Celsius

Static Altitude Methods ¶

static float AP_Baro::get_altitude_from_pressure(float pressure) const¶

Calculate altitude from pressure (barometric formula).

Parameters:: pressure – Pressure in Pa
Returns:: Altitude in meters

static float AP_Baro::get_sealevel_pressure(float pressure, float altitude) const¶

Calculate sea level pressure from measured pressure and altitude.

Parameters:

pressure – Measured pressure in Pa
altitude – Current altitude in meters

Returns:

Sea level pressure in Pa

float AP_Baro::get_altitude_difference(float base_pressure, float pressure) const¶

Calculate altitude difference between two pressures.

Parameters:

base_pressure – Base pressure in Pa
pressure – Current pressure in Pa

Returns:

Altitude difference in meters

EAS/TAS Conversion ¶

static float AP_Baro::get_EAS2TAS_for_alt_amsl(float alt_amsl)¶

Get Equivalent Airspeed to True Airspeed ratio for given altitude.

Parameters:: alt_amsl – Altitude above mean sea level in meters
Returns:: EAS2TAS ratio

static float AP_Baro::get_air_density_for_alt_amsl(float alt_amsl)¶

Get air density ratio for given altitude.

Parameters:: alt_amsl – Altitude above mean sea level in meters
Returns:: Air density ratio (relative to sea level)

Usage Example ¶

#include <AP_Baro.h>

AP_Baro *baro;

void setup() {
    baro = AP_Baro::get_singleton();
    if (baro == nullptr) {
        Serial.println("Baro not available");
        return;
    }

    // Calibrate barometer on startup
    baro->calibrate(true);
}

void loop() {
    // Update barometer
    baro->update();

    // Check health
    if (baro->healthy()) {
        // Get altitude
        float altitude = baro->get_altitude();
        Serial.printf("Altitude: %.2f m\n", altitude);

        // Get pressure
        float pressure = baro->get_pressure();
        Serial.printf("Pressure: %.2f Pa\n", pressure);

        // Get temperature
        float temperature = baro->get_temperature();
        Serial.printf("Temperature: %.2f C\n", temperature);

        // Get climb rate
        float climb_rate = baro->get_climb_rate();
        Serial.printf("Climb Rate: %.2f m/s\n", climb_rate);
    }
}