Simulation Frame Comparisons Need a Time as Well as a Name

A simulation screenshot can show a robot and a target in the same scene, but it does not reveal which coordinate transform was used or when that transform was valid. A useful simulation record identifies the frames, the time associated with the data and the software environment before drawing conclusions from a displayed position.

Record the frame pair and the question being asked

Write down the source frame, target frame, observed object and intended comparison. A position relative to a camera is not automatically the same thing as a position relative to a robot base. Include the simulation model, ROS 2 version, relevant package version and the way the example was started, subject to the project’s information-sharing rules.

The ROS 2 Jazzy tf2 concepts documentation describes maintaining relationships among coordinate frames over time. It explains a software framework, not a calibration certificate for a physical robot. A frame name alone does not establish that the simulated geometry matches an installed sensor or machine.

Distinguish a timestamp from a screenshot time

A screenshot may have a capture time, while a message or transform has its own timestamp. Record both when they are available, and identify which clock or simulation context the project uses. Do not assume that two pieces of data were produced at the same instant simply because they appear in one screen capture.

If an example has been paused, restarted or replayed, note that event. Preserve the relevant logs and configuration where authorised. An incomplete time record should be labelled incomplete rather than repaired with a guessed value from another run.

Understand a time-specific lookup

The ROS 2 Jazzy tutorial on using time with tf2 in C++ explains requesting a transform for a specified time and illustrates waiting for a transform to become available. The tutorial also describes a special time value used to request the latest available transform. These details are specific to the documented API and example; applications should consult the documentation for their own version.

For an investigation, record whether the example requested a particular time or the latest available transform, and what result or error was actually returned. Do not turn a missing transform into a claim that a sensor is defective without further evidence. A software lookup result is only one part of the context needed to interpret the displayed scene.

Use a hypothetical replay comparison

Imagine a learner compares two simulated runs and sees a target marker in different positions. The learner records the frame names, timestamps, model versions and any restart between the captures. If one capture lacks a timestamp, the result is “insufficient context to compare,” not proof that the simulated robot moved incorrectly. This is a hypothetical learning example, not a report about a real system.

When the exercise is repeated, document which input or setting changed and retain the earlier evidence. Do not edit a previous record to make the two runs appear consistent. A comparison can remain unresolved until the missing frame or time information is available.

The reviewer can also list the observations that would make the comparison more useful: the original message timestamp, the requested frame pair, a description of the clock in use, and the version of the simulation scenario. Those items form a request for evidence, not a diagnosis. If a field cannot be recovered, the final note should say which conclusion remains uncertain and why.

Keep model geometry and time evidence distinct

Model files describe aspects of the simulated robot, while transforms and message timestamps describe relationships used during a run. A mismatch may involve the model, the frame definitions, the data source or another part of the environment. The record should preserve these as separate questions rather than attributing the result to one component in advance.

The site’s article on visual and collision models discusses another modelling distinction. A model that looks convincing does not by itself demonstrate correct timing, collision behaviour or physical calibration. Each claim needs evidence from the relevant implementation and test.

Prepare a reproducible handover

Share the permitted model revision, launch instructions, relevant frame names, time context and selected output with the person reviewing the exercise. Include any missing information and the exact observation that prompted the review. Protect credentials and customer data, and follow the project’s access rules when transferring files. Confirm that the recipient can identify which output came from which run, rather than sending a collection of unnamed screenshots.

The industry information section provides background. This guide concerns documentation of simulation evidence; work on a physical robot requires equipment-specific procedures, authorised personnel and appropriate safety controls.