Using MAVLink Inspector to Validate ArduPilot Telemetry Data

TL;DR: Use the MAVLink Inspector to confirm telemetry data by checking the GPS.Status field against expected values. Look for a GPS.Status value of 3 or higher for a good GPS fix, and adjust GPS_HDOP_GOOD to keep HDOP values below 1.0 for optimal navigation performance.

What MAVLink Inspector Actually Is in the Log

MAVLink Inspector is a tool for visualizing and analyzing MAVLink messages in real-time, providing insights into telemetry data from your ArduPilot system. The relevant log messages can be summarized as follows:

MSG_NAME  TimeUS  Status  Lat  Lng  Alt  Spd  HDop

- TimeUS: Timestamp of the message in microseconds. - Status: Indicates the GPS fix status. - Lat: Latitude of the drone. - Lng: Longitude of the drone. - Alt: Altitude above sea level. - Spd: Ground speed of the drone. - HDop: Horizontal dilution of precision, indicating the accuracy of the GPS fix.

Confirming It in Mission Planner

To access MAVLink Inspector in Mission Planner, follow these steps: 1. Open Mission Planner. 2. Connect to your drone. 3. Click on the "Flight Data" tab. 4. Press Ctrl + F to open the MAVLink Inspector. In the MAVLink Inspector, you can plot several fields to analyze telemetry data. The following fields are crucial for validating GPS performance: - GPS.Status - GPS.Lat - GPS.Lng - GPS.Alt - GPS.HDop

Confirming It in MAVExplorer

To analyze telemetry data in MAVExplorer, you can run the following command:

MAV> graph GPS.Lat GPS.HDop

This command will generate a plot comparing the latitude and HDOP values over time. A stable latitude with HDOP values consistently below 1.0 indicates reliable GPS performance.

Why MAVLink Inspector Issues Happen — Ranked by What We See Most Often

1. GPS Glitch: Identified by ERR Subsys=11 ECode=2. Causes include poor satellite visibility or interference. More details can be found in our GPS Glitch post.
2. High HDOP Values: HDOP exceeding 2.0 reflects poor positioning accuracy. This often occurs in urban environments or under heavy foliage.
3. Inconsistent Altitude Readings: Fluctuations in GPS.Alt may indicate issues with barometric pressure sensors or GPS signal instability.
4. Incorrect Lat/Lng Readings: Occurs due to satellite lock failures or configuration errors, which can be diagnosed through GPS.Status.

Fixes for MAVLink Inspector Issues

1. Ensure your drone is in an open area to improve satellite visibility and reduce interference.
2. Adjust the GPS_HDOP_GOOD parameter to a lower value to ensure your system recognizes HDOP values above this threshold as problematic.
3. Inspect and calibrate your barometer to ensure accurate altitude readings.
4. Ensure proper configuration and calibration of your GPS receiver to prevent incorrect latitude and longitude readings.

When This Isn't Actually a MAVLink Inspector Issue

- High HDOP values may not always indicate a MAVLink problem; they can result from environmental conditions. - Satellite lock failures can stem from hardware issues unrelated to MAVLink messaging. - Erratic altitude readings may also result from physical damage to the barometer rather than a MAVLink communication failure.

When LogHat Helps — and When It Doesn't

LogHat excels at analyzing telemetry data from ArduPilot, allowing us to easily visualize and interpret MAVLink messages. However, it cannot directly resolve hardware issues or environmental factors affecting telemetry data quality.

What is MAVLink Inspector?

A tool for visualizing and analyzing MAVLink messages in real-time.

How do I access MAVLink Inspector?

In Mission Planner, press Ctrl-F and click the 'MAVLink Inspector' button.

How can I troubleshoot GPS issues using MAVLink Inspector?

Check the GPS.Status and HDop values to identify potential problems.

What do HDOP values indicate?

HDOP values indicate the accuracy of GPS positioning; lower values are better.

What can cause GPS glitches?

GPS glitches can be caused by poor satellite visibility or interference.

How do I improve GPS performance?

Ensure your drone is in an open area and calibrate your GPS system.

What should I do if altitude readings are fluctuating?

Inspect and calibrate your barometer for accurate altitude measurements.