how to subscribe to data from any MCAP file generalised in a 3D panel .

[JaplaVikash]

I need help understanding how to subscribe to data from any MCAP file in a 3D panel. I am currently creating a custom panel using a custom schema, and it works correctly when I upload data that matches this schema.

However, when I upload a general MCAP file, the data appears in the default 3D panel, but not in my custom panel.

I want to generalize the subscription logic in my custom panel so it can read and display data from any MCAP file, regardless of the schema. Could someone please guide me on how to achieve this? Also, please suggest where I can find the relevant code for subscribing to MCAP data.

[aneuwald-ctw]

Hey @JaplaVikash, thanks for reaching out!

So, just to be clear, the panels ALWAYS subscribe to "topics", not schemas. What the 3D does is read all topics, check their schemas (or schemas that will be converted to by message converters) and then subscribe to topics with the desired schemas. But ALWAYS subscribe to topics.

If you want to have the same behavior on your custom panel, you should do the same. Watch the topics, do some logic to filter which topic satisfies your needs and subscribe to it.

Here is an example of how to watch all topics and how to iterate over them:

You can check in the 3D panel code where this logic is done:

lichtblick/packages/suite-base/src/panels/ThreeDeeRender/ThreeDeeRender.tsx

Lines 382 to 446 in 9fc03ea

	// Build a list of topics to subscribe to
	const [topicsToSubscribe, setTopicsToSubscribe] = useState<Subscription[] | undefined>(undefined);
	useEffect(() => {
	if (!topics) {
	setTopicsToSubscribe(undefined);
	return;
	}
	const newSubscriptions: Subscription[] = [];
	const addSubscription = (
	topic: Topic,
	rendererSubscription: RendererSubscription,
	convertTo?: string,
	) => {
	let shouldSubscribe = rendererSubscription.shouldSubscribe?.(topic.name);
	if (shouldSubscribe == undefined) {
	if (config.topics[topic.name]?.visible === true) {
	shouldSubscribe = true;
	} else if (config.imageMode.annotations?.[topic.name]?.visible === true) {
	shouldSubscribe = true;
	} else {
	shouldSubscribe = false;
	}
	}
	if (shouldSubscribe) {
	newSubscriptions.push({
	topic: topic.name,
	preload: rendererSubscription.preload,
	convertTo,
	});
	}
	};
	for (const topic of topics) {
	for (const rendererSubscription of topicSubscriptions.get(topic.name) ?? []) {
	addSubscription(topic, rendererSubscription);
	}
	for (const rendererSubscription of schemaSubscriptions.get(topic.schemaName) ?? []) {
	addSubscription(topic, rendererSubscription);
	}
	for (const schemaName of topic.convertibleTo ?? []) {
	for (const rendererSubscription of schemaSubscriptions.get(schemaName) ?? []) {
	addSubscription(topic, rendererSubscription, schemaName);
	}
	}
	}
	// Sort the list to make comparisons stable
	newSubscriptions.sort((a, b) => a.topic.localeCompare(b.topic));
	setTopicsToSubscribe((prev) => (_.isEqual(prev, newSubscriptions) ? prev : newSubscriptions));
	}, [
	topics,
	config.topics,
	// Need to update subscriptions when imagemode topics change
	// shouldSubscribe values will be re-evaluated
	config.imageMode.calibrationTopic,
	config.imageMode.imageTopic,
	schemaSubscriptions,
	topicSubscriptions,
	config.imageMode.annotations,
	// Need to update subscriptions when layers change as URDF layers might subscribe to topics
	// shouldSubscribe values will be re-evaluated
	config.layers,
	]);