the Robot Construction Kit

... at Runtime

At runtime, components that are using the stream aligner behave more or less like normal components (when one considers that they can introduce latency in the data processing chain, of course).

The integrator of such a component should, though, be careful to set the stream periods properly. As noted in the data processing overview:

Because processing based on the stream aligner is based on the fact that samples are passed in-order, the stream aligner must drop samples that arrive “in the past”, i.e. that arrive with an earlier timestamp that the last sample “played” by the stream aligner. So, it is better to give a period that is lower than the actual sensor period so that the aligner does not drop samples unnecessarily.

The choice of the timeout is also important, but not so critical: the timeout is a last resort mean to keep the data flowing. One should prefer using advanced means of monitoring.


The stream aligner allows to export a pretty complete statistics structure of type /aggregator/StreamAlignerStatus, that informs the outside world about the general aligner behaviour. The oroGen plugin exports that structures on an output port called stream_aligner_status that exports this data structure. By default, it is exported every second but this can be configured with the stream_aligner_status_period property.

The data structure is very comprehensive. However, the main “sanity” variables are the dropped count. See the type documentation (linked above) for more details.