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Relative Barometric Altitude #16

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Relative Barometric Altitude #16

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94d9141
Updated altitude estimation code to be relative rather than from sea …
dmanslick May 27, 2026
16bb437
Updatec constants and BMP581 struct
dmanslick Jun 5, 2026
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6 changes: 4 additions & 2 deletions Ganesha_II_V2/Core/Inc/bmp581.h
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Original file line number Diff line number Diff line change
Expand Up @@ -20,21 +20,23 @@
#define TROPOPAUSE_BASE_ALTITUDE 11000.0f // m
#define STRATOSPHERE_MIDDLE_BASE_ALTITUDE 20000.0f // m

#define TROPOSPHERE_LAPSE_RATE -0.0065f // K/m
#define TROPOSPHERE_LAPSE_RATE 0.0065f // K/m
#define UPPER_STRATOSPHERE_LAPSE_RATE 0.001f // K/m

struct BMP581 {
struct bmp5_dev device;
struct bmp5_osr_odr_press_config odr_config;
struct bmp5_int_source_select int_config;
I2C_HandleTypeDef *hi2c;
float starting_altitude;
};

BMP5_INTF_RET_TYPE read_i2c(uint8_t reg_addr, uint8_t *reg_data, uint32_t length, void *intf_ptr);
BMP5_INTF_RET_TYPE write_i2c(uint8_t reg_addr, const uint8_t *reg_data, uint32_t length, void *intf_ptr);
int8_t bmp581_init(struct BMP581 *bmp581, I2C_HandleTypeDef *handle);
int8_t bmp581_update_data(struct BMP581 *bmp581, struct bmp5_sensor_data *data);
int8_t bmp581_get_power_mode(struct BMP581 *bmp581, enum bmp5_powermode *powermode);
float bmp581_estimate_altitude_msl(struct BMP581 *bmp581, struct bmp5_sensor_data *data);
void bmp581_init_altitude_estimator(struct BMP581 *bmp581, struct bmp5_sensor_data *data);
float bmp581_estimate_altitude_relative(struct BMP581 *bmp581, struct bmp5_sensor_data *data);

#endif
47 changes: 24 additions & 23 deletions Ganesha_II_V2/Core/Src/bmp581.c
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Original file line number Diff line number Diff line change
Expand Up @@ -80,39 +80,40 @@ int8_t bmp581_update_data(struct BMP581 *bmp581, struct bmp5_sensor_data *data)
return bmp5_get_sensor_data(data, &(bmp581->odr_config), &(bmp581->device));
}

static inline float calc_altitude_troposphere_msl(float pressure) {
float exponent = (-GAS_CONSTANT * TROPOSPHERE_LAPSE_RATE) / (GRAVITY_ACCEL * AIR_MOLAR_MASS);
float pressure_ratio = pressure / STANDARD_SEA_LEVEL_PRESSURE;
float power_term = powf(pressure_ratio, exponent) - 1;

return (STANDARD_SEA_LEVEL_TEMP / TROPOSPHERE_LAPSE_RATE) * power_term;
static inline float troposphere_calc(float pressure) {
const float exponent = (-GAS_CONSTANT * TROPOSPHERE_LAPSE_RATE) / (GRAVITY_ACCEL * AIR_MOLAR_MASS);
return (STANDARD_SEA_LEVEL_TEMP / TROPOSPHERE_LAPSE_RATE) * (powf(pressure / STANDARD_SEA_LEVEL_PRESSURE, exponent) - 1.0f);
}

static inline float calc_altitude_lower_stratosphere_msl(float pressure) {
float log_ratio = logf(pressure / TROPOPAUSE_PRESSURE);
float scale_factor = (GAS_CONSTANT * STRATOSPHERE_BASE_TEMP) / (GRAVITY_ACCEL * AIR_MOLAR_MASS);

return TROPOPAUSE_BASE_ALTITUDE - (scale_factor * log_ratio);
static inline float lower_stratosphere_calc(float pressure) {
const float scale_height = (GAS_CONSTANT * STRATOSPHERE_BASE_TEMP) / (GRAVITY_ACCEL * AIR_MOLAR_MASS);
return TROPOPAUSE_BASE_ALTITUDE + scale_height * logf(TROPOPAUSE_PRESSURE / pressure);
}

static inline float calc_altitude_upper_stratosphere_msl(float pressure) {
float exponent = (-GAS_CONSTANT * UPPER_STRATOSPHERE_LAPSE_RATE) / (GRAVITY_ACCEL * AIR_MOLAR_MASS);
float pressure_ratio = pressure / STRATOSPHERE_MIDDLE_PRESSURE;
float power_term = powf(pressure_ratio, exponent) - 1;

return STRATOSPHERE_MIDDLE_BASE_ALTITUDE + (STRATOSPHERE_BASE_TEMP / UPPER_STRATOSPHERE_LAPSE_RATE) * power_term;
static inline float upper_stratosphere_calc(float pressure) {
const float exponent = (-GAS_CONSTANT * UPPER_STRATOSPHERE_LAPSE_RATE) / (GRAVITY_ACCEL * AIR_MOLAR_MASS);
const float term = powf(pressure / STRATOSPHERE_MIDDLE_PRESSURE, exponent) - 1.0f;
return STRATOSPHERE_MIDDLE_BASE_ALTITUDE + (STRATOSPHERE_BASE_TEMP / UPPER_STRATOSPHERE_LAPSE_RATE) * term;
}

float bmp581_estimate_altitude_msl(struct BMP581 *bmp581, struct bmp5_sensor_data *data) {
if (data->pressure > TROPOPAUSE_PRESSURE) {
return calc_altitude_troposphere_msl(data->pressure);
} else if (data->pressure > STRATOSPHERE_MIDDLE_PRESSURE) {
return calc_altitude_lower_stratosphere_msl(data->pressure);
static inline float pressure_to_isa_altitude(float pressure) {
if (pressure > TROPOPAUSE_PRESSURE) {
return troposphere_calc(pressure);
} else if (pressure > STRATOSPHERE_MIDDLE_PRESSURE) {
return lower_stratosphere_calc(pressure);
} else {
return calc_altitude_upper_stratosphere_msl(data->pressure);
return upper_stratosphere_calc(pressure);
}
}

void bmp581_init_altitude_estimator(struct BMP581 *bmp581, struct bmp5_sensor_data *data) {
bmp581->starting_altitude = pressure_to_isa_altitude(data->pressure);
}

float bmp581_estimate_altitude_relative(struct BMP581 *bmp581, struct bmp5_sensor_data *data) {
return pressure_to_isa_altitude(data->pressure) - bmp581->starting_altitude;
}

int8_t bmp581_get_power_mode(struct BMP581 *bmp581, enum bmp5_powermode *powermode) {
return bmp5_get_power_mode(powermode, &(bmp581->device));
}
14 changes: 10 additions & 4 deletions Ganesha_II_V2/Core/Src/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -175,8 +175,9 @@ void HAL_GPIO_EXTI_Callback(uint16_t pin) {
}

struct Orientation_Estimator estimator;
uint8_t estimator_init = 0;
uint8_t orientation_estimator_initialized = 0;

uint8_t altitude_estimator_initialized = 0;
/* USER CODE END 0 */

/**
Expand Down Expand Up @@ -318,9 +319,9 @@ int main(void)
packet.angular_velocity_y_rads = bmi088_convert_gyro_axis_data(&bmi088, bmi088_gyro_data.y);
packet.angular_velocity_z_rads = bmi088_convert_gyro_axis_data(&bmi088, bmi088_gyro_data.z);

if (!estimator_init) {
if (!orientation_estimator_initialized) {
orientation_estimator_reset_from_accel(&estimator, packet.acceleration_x_mss, packet.acceleration_y_mss, packet.acceleration_z_mss);
estimator_init = 1;
orientation_estimator_initialized = 1;
}

orientation_estimator_add_gyro_reading(
Expand All @@ -347,7 +348,12 @@ int main(void)
bmp581_update_data(&bmp581, &bmp_data);
}

packet.barometer_hMSL_m = bmp581_estimate_altitude_msl(&bmp581, &bmp_data);
if (!altitude_estimator_initialized && (bmp_data.pressure && bmp_data.temperature)) {
bmp581_init_altitude_estimator(&bmp581, &bmp_data);
altitude_estimator_initialized = 1;
}

packet.barometer_hMSL_m = bmp581_estimate_altitude_relative(&bmp581, &bmp_data);
packet.temperature_c = bmp_data.temperature;

if (dumb_timer_done(&camera_timer)) {
Expand Down