fix(tracking_object_merger): flip main object direction when the object velocity is backward.

[technolojin]

Description

Issue: At the

Issue tracker (Tier4 internal): https://tier4.atlassian.net/browse/RT1-5257

Tests performed

Before fix:

tracker_merge_reversed_obj.mp4

The multi-object tracker (mainly from lidar, blue box) has opposite direction and when the radar object is also used to obtain velocity, the merger trusts the orientation of the main object (lidar object). as result, the merged object (yellow box) has the reversed direction.

After fix:

tracker_merge_reversed_obj_fixed_2.mp4

Since the merger assumes the object is driving forward, the merger will flip the velocity vector and its orientation when the incoming object has negative x velocity (driving backward).

Effects on system behavior

The merger result will have more stable result when MOT tracker has orientation error.
The merger cannot output backward-driving vehicle correctly.

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