Clean up temperature msg fields #24272

haumarco · 2025-01-30T10:51:01Z

Solved Problem

Currently, multiple temperature measurements are used across different functionalities to represent ambient temperature. This creates ambiguity regarding which temperature measurement should be designated as vehicle_temperature. We lack dedicated temperature sensors or topics to consistently rely on a single source.

Solution

Implement a prioritized selection of temperature sensors. When an external airspeed sensor is available, its temperature is used as the primary source. If an external barometer is present, its temperature serves as the secondary option. The temperature from the internal barometer is disregarded due to its unreliability, which is caused by inconsistent PCB heat dissipation across different flight controllers.

Changelog Entry

Create a distinct ambient_temperature field in the VehicleAirData message.

Alternatives

An alternative approach would be to create a dedicated temperature uORB topic to centralize ambient temperature data.

Test Coverage

Tested with various setups and hardcoded measurements in simulation environments to ensure reliability and accuracy.

github-actions · 2025-01-30T13:05:38Z

🔎 FLASH Analysis

px4_fmu-v5x [Total VM Diff: -96 byte (-0 %)]

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px4_fmu-v6x [Total VM Diff: -72 byte (-0 %)]

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--------------  -------------- 
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Updated: 2025-02-06T17:33:25

sfuhrer · 2025-01-30T16:28:09Z

src/modules/mavlink/streams/HIGH_LATENCY2.hpp

+	{
+		vehicle_air_data_s air_data;
+
+		if (_vehicle_air_data_sub.update(&air_data)) {


This will need a small edit of the comment in the MAVLink message.
"Air temperature from airspeed sensor" is no longer valid.

mavlink/mavlink#2210

@sfuhrer It doesn't work that way - if this PR merges PX4 is no longer compliant with the MAVLink specification. The message itself is fine :-)

Whether we can update the message in MAVLink depends on whether there is a semantic difference that matters to consumers. I don't know, but that requires agreement with other stakeholders.

I know, and we'll update the wording on the mavlink RP. Never the less, we're convinced that this is the right approach.
@haumarco to be compliant with the mavlink message we can for now also subscribe to differential_pressure.temperature here.

src/modules/sensors/vehicle_air_data/VehicleAirData.cpp

src/drivers/uavcan/sensors/airspeed.cpp

sfuhrer · 2025-02-04T17:03:18Z

msg/VehicleAirData.msg

 float32 baro_pressure_pa		# Absolute pressure in Pascals
+float32 ambient_temperature		# Abient temperature in degrees Celsius


Should we add a flag for the source of this field? Differential pressure, external baro, default ambient air temperature?

ok. added enum for temperature source
0: Default value, i.e. 15°C
1: External baro
2: Airspeed

Maybe "default" should be more like "not available" (N/A)?

Do you mean I should only change the naming from Default to NA or also change the Default/NA data?
I want to have the default temperature (15 deg) to be published when we dont have a external sensor. Also to avoid multiple definitions of "default" temperature values at the subscribers as mentioned in my previous comment. #24272 (comment)

Can you clarify if you simply care about the naming or also the value? NA would not be a good match IMO when I still enter a default value

sfuhrer · 2025-02-04T17:08:29Z

src/modules/mavlink/streams/HIGHRES_IMU.hpp

@@ -193,7 +193,7 @@ class MavlinkStreamHighresIMU : public MavlinkStream
 			msg.abs_pressure = air_data.baro_pressure_pa;
 			msg.diff_pressure = differential_pressure.differential_pressure_pa;
 			msg.pressure_alt = air_data.baro_alt_meter;
-			msg.temperature = air_data.baro_temp_celcius;
+			msg.temperature = air_data.ambient_temperature;


Shouldn't that field be filled with the IMU temperature? How about subscribing to vehicleImuStatus.msg/temperature_accel or _gyro?

The temperature field in HIGHRES_IMU seems a bit arbitrary. Since it takes the other data-fields from the air_data, I would keep it like that.

If the user wants the IMU data, one can access it over SCALED_IMU or RAW_IMU

sfuhrer · 2025-02-04T17:09:28Z

src/modules/mavlink/streams/HIGH_LATENCY2.hpp

+		vehicle_air_data_s air_data;
+
+		if (_vehicle_air_data_sub.update(&air_data)) {
+			_temperature.add_value(air_data.ambient_temperature, _update_rate_filtered);


Should we only publish a value if it's actually coming a sensor and is not the hard coded 15°C?

As I now also added the enum to specify the temperature source to the msg, I think having the default value published can be useful. It avoids a sanity check and definition of another default temperature at the Subscriber...

haumarco requested a review from sfuhrer January 30, 2025 10:51

haumarco added 3 commits January 30, 2025 13:52

remove temp field from airspeed.msg, adjust temp selection

b120633

temp-sensor hirarchy: airspeed, ext. baro, default value

269413a

directly use diff-press or baro temp in true-airspeed calc

695bfb9

haumarco force-pushed the pr_clean_temperature_usage branch from e60a339 to 695bfb9 Compare January 30, 2025 12:58

sfuhrer reviewed Jan 30, 2025

View reviewed changes

improve clarity

e18e01e

haumarco mentioned this pull request Feb 3, 2025

Adjust HIGH_LATENCY2 temperature_air field description mavlink/mavlink#2210

Open

sfuhrer reviewed Feb 4, 2025

View reviewed changes

add enum for temperature source in VehicleAirData.msg

6ffcb72

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Clean up temperature msg fields #24272

Clean up temperature msg fields #24272

haumarco commented Jan 30, 2025

github-actions bot commented Jan 30, 2025 •

edited

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sfuhrer Jan 30, 2025

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haumarco Feb 6, 2025

		float32 baro_pressure_pa # Absolute pressure in Pascals
		float32 ambient_temperature # Abient temperature in degrees Celsius

Clean up temperature msg fields #24272

Are you sure you want to change the base?

Clean up temperature msg fields #24272

Conversation

haumarco commented Jan 30, 2025

Solved Problem

Solution

Changelog Entry

Alternatives

Test Coverage

github-actions bot commented Jan 30, 2025 • edited Loading

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github-actions bot commented Jan 30, 2025 •

edited

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