IMU Covariances: Distinguish Unknown From Unavailable
Interpret ROS 2 IMU covariance markers and units correctly, separating unknown uncertainty from an estimate the device does not provide. This guide concerns robot integration and delivery review. The proposed observations are editorial assessment guidance, grounded in the linked original documentation and subject to the deployed version. They do not describe an on-site test of a particular machine or establish whole-system acceptance from a single interface response.
Check each measurement separately
Review orientation, angular velocity and linear acceleration with their respective covariance fields. One available quantity does not establish availability of every estimate in the message. The definition supplies separate matrices, and the consumer should interpret them separately. Retain original samples and driver capabilities rather than only one combined healthy indication selected by a display.
For this review, identify the delivered device, software and configuration revisions first. Record unsupported, disabled and untested capabilities separately. Evidence from another model is useful context, but cannot establish what the delivered combination actually provides. Keep the original input beside the settings used to interpret it.
Separate zero matrices from unavailable estimates
The definition interprets an all-zero covariance as unknown uncertainty and a first element of minus one as no estimate for that quantity. Unknown does not mean zero error, and unavailable should not become a measured zero. Record the consumer’s handling of both cases and the source of any additional uncertainty assumption it requires.
Retain the original input and the reason for the decision, rather than a successful screenshot alone. Change only the variables agreed for the comparison, and keep the before-and-after configuration. List conditions that were not exercised explicitly; they should not silently become part of the accepted operating range.
Review units and covariance association
The definition uses metres per second squared for acceleration and radians per second for angular velocity. Raw values expressed in gravity units or degrees per second need appropriate treatment. Retain conversion and covariance provenance. Separate measurement conversion from uncertainty interpretation so changing numeric units does not leave the related matrix with an unexplained or incompatible meaning.
Use the three illustrated observations as starting questions, rather than as diagnoses of an installation that has not been inspected. Check record completeness, units and identity before selecting the next observation. An unresolved result is more informative than a confident explanation assembled from missing fields or unrelated test runs.
Inspect adoption of missing estimates
In isolated review, retain distinct cases for available estimates, unknown covariance and unavailable quantities, observing the algorithm’s actual input choices. Parsing success is insufficient; identify ignored fields and additional assumptions. Do not fabricate a smooth-looking orientation or acceleration sequence merely to populate a chart when the device supplies no corresponding measurement or estimate.
Let the site owner choose an approved isolated way to exercise relevant exceptions. Record normal operation, the exceptional condition and recovery separately. The purpose is to establish how the application recognises and explains untrustworthy input, without requiring production equipment to act on deliberately invalid results.
Deliver capability and uncertainty provenance
Deliver device and driver revisions, available estimates, unit conversions, covariance basis and unresolved items. Revisit consumer handling after filtering or hardware changes. Accuracy claims require suitable independent evidence; an all-zero matrix or many displayed decimal places cannot establish ideal sensor accuracy or a quantified uncertainty that the interface itself reports as unknown.
Deliver the configuration, representative samples, result table and unresolved questions together. Agree who reviews subsequent changes. The receiving team should be able to select one conclusion and trace it back to its input and decision path without relying on the original author to reconstruct the missing steps.
Original documentation and further reading
Continue with related articles in this section, or use selection guides to prepare the next review. Apply the device-specific documentation and agreed operating conditions when implementing a test.