Streaming Interface

[ThomasNaderBMW]

#### Reference to a related issue in the repository https://github.com/OpenSimulationInterface/open-simulation-interface/issues/700

Add a description

A streaming interface is needed for e.g. powering a graphics engine with dynamic changing data in a higher frequency.

Some questions to ask: What is this change? New generic interface for powering other components with dynamic data. Is this a bug fix or a feature? Does it break any existing functionality or force me to update to a new version? It is a new feature. How has it been tested? It is tested with a similar interrface.

Take this checklist as orientation for yourself, if this PR is ready for the Change Control Board:

• [ ] My suggestion follows the style and contributors guidelines.
• [ ] I have taken care about the message documentation and the fields and enums documentation.
• [ ] I have done the DCO signoff.
• [ ] My changes generate no errors when passing CI tests.
• [ ] I have successfully implemented and tested my fix/feature locally.
• [ ] Appropriate reviewer(s) are assigned.

If you can’t check all of them, please explain why. If all boxes are checked or commented and you have achieved at least one positive review, you can assign the label ReadyForCCBReview!

[ThomasNaderBMW]

// Approach 1: is_obsolete flags inside the messages (example see osi_object.proto)

• need to change all the messages, clarify for what it is clearly used  + however, if user does not care, it can be simply ignored
• all information at one place

// Approach 2: Is shown below, id_lists (also for traffic lights etc.) //repeated Identifier obsolete_moving_object_id = x;

• this is the least impact. volume of data, and changes to message

// Approach 3: This message with an enum describing if content is to update or to delete.

• two top level messages

[globberwops]

Approach 1)

Pros:

• perfectly backwards compatible
• value can be completely ignored
• no data overhead if not sent
• best information locality
• easy to use in impl

Cons:

• Needs unambiguous documentation

Approach 2)

Pros:

• perfectly backwards compatible
• value can be completely ignored
• no data overhead if not sent
• least impact

Cons:

• Needs external knowledge
• bad information locality
• comparison of multiple data sources

[ThomasNaderBMW]

Regarding realising a streaming interface, these are the open questions/points: - Why not the approach sending GroundTruth cyclic (with a delta encoding flag) + a obsolete_id-Message? Or an inherited mechanism?

• HostVehicleData also part of the message? ==> So far yes
• HostVehicleData: Can all the data be changed or is it allowed?
• Are the so far included submessages in the PR correct? Also the approach to extend in the future
• Environmental Subconditions are solved inside EnvironmentalConditions, not on a higher level
• Descriptions need to be reworked
• Documentation is not enough at the moment
• The name of osi_streaming.proto is not 100% correct. How would you name it? One idea was more closer symetric delta..
• What about controlling the external part?
• What if a new agent pops up, how does he know the initial dataset?

[thomassedlmayer]

Refering to earlier discussions, this interface was planned to improve performance for use cases like visualization or similar but did not intend to be a "real"/full delta encoding for OSI, right? So I guess one reason why we opted for a separate message for this interface and did not aim to use the GroundTruth message with some indicator flag (+ obsolete_id list) may be that it would not be accidently misunderstood/misused as delta encoding. In contrast to delta encoding, this "partial update" approach would enable to send updates only for objects that are considered relevant for the receiver (from sender point of view) and omit non-relevant object updates, right? It would not necessarily result in a complete representation of the groundtruth at the receiver. You would not know what happened to objects that were not included in the update.

I'd like to clarify which of the following variants we are discussing:

• Send relevant objects (even if unchanged), not send non-relevant objects, add objects to obsolete_id list that just became obsolete/non-relevant
• Send only objects that changed, not send unchanged objects, add objects to obsolete_id list that are not part of GroundTruth anymore at all (= more like real delta encoding as alternative to current way of sending complete OSI GroundTruth)
• Something else?

I thought, initially we would aim for the first variant or did I understand something wrong? I think it would make sense to have some precise definition of what we want to achieve with this interface and how it would work in practice because for me it is quite confusing and unclear what the general understanding of the group concerning this topic is.

Also, I think we agreed on not using delta updates on fields like position etc., right? So an update message still contains the complete position/orientation/etc. values just like in the "original" groundtruth. That's why I think, we should not include "delta" in the name. It could be easily misunderstood IMO.

@ThomasNaderBMW I did not yet receive an invitation for the separate meeting to discuss the streaming interface. What was the date/time again?

[ThomasNaderBMW]

@thomassedlmayer : Thank you very much for your input.

I sent you the meeting, but you should already have gotten it. It is on 2nd May.

I agree on, that the whole object (moving object e.g.) has to be sent if a single value changes.

[ThomasNaderBMW]

Special Meeting Performance & Packaging: Regarding realising a streaming interface, these are the open questions/points:

• Why not the approach sending GroundTruth cyclic (with a delta encoding flag) + a obsolete_id-Message? Or an inherited mechanism? ==>Not intended as delta encoding message (concerned with bandwith), it is more a streaming update message (concerned with latency, minimizing it). ==>Two Messages because semantics of classical GT-mechanism and Streaming-mechanism are too different to put it alltogether. HostVehicleData also part of the message? ==> So far yes. But needs to be repeated HostVehicleData: Can all the data be changed or is it allowed? ==> Yes can be changed and is allowed. Are the so far included submessages in the PR correct? Also the approach to extend in the future. Environmental Subconditions are solved inside EnvironmentalConditions, not on a higher level. Descriptions need to be reworked. Documentation is not enough at the moment. The name of osi_streaming.proto is not 100% correct. How would you name it? One idea was more closer symetric delta.. ==> It is not delta encoding any more. So streaming is correct. But better suggestions are welcome! What about controlling the external part? What if a new agent pops up, how does he know the initial dataset? ==> If you want to use it for that you need to se the first frame. To the initial setup data/Resync: ==> Next Meeting Performance & Packaging

[ThomasNaderBMW]

Performance & Packaging, 04.05.23: New Open Points:

• Sending new objects if they are calculated new or if a property has changed?
• First time message is being sent, how to handle that?
• Mention an e.g. use case in the description
• Documentation figure needs to be done (M. Lemmer sends it to T. Nader)

[ThomasNaderBMW]

CCB Review, 19.06.23:

• Can be merged.
• DCO-Sign off will be done by Pierre Mai.