Ground truth id repeated in DetectedItemHeader

[jruebsam]

Having a look at the DetectedItemHeader definition I realised that ground_truth_id is defined as a repeated message. Is this desired behavior, since e.g. vor a moving object only a single id is defined ?

[thomassedlmayer]

I think there were some protobuf issues differentiating intended empty numeric fields. For numeric types the default/empty state is 0, which could also be some object id. I guess this issue was solved by using a repeated field and giving the option to have 0 items in the list indicating that no object is linked?

In the RadarDetection message there also is an object id reference which is not repeated but optional. Though here the max uint64 value is used to tell apart an actual intended lack of referenceable object.

[thomassedlmayer]

I talked to Pierre about this and he told me that it most probably was intended to allow referencing multiple ground truth references to merge multiple ground truth objects into a single detected object. This may especially make sense for some stationary objects. This is just not stated properly in the documentation.

My first guess that this may have been a fix to the protobuf issue concerning empty numeric field was wrong since ground_truth_id is not a numeric field but is of type Identifier.