- Use a "Bus Selector" block to pull out the "ConfirmedTracks" bus from the Multi-Object Tracker output (gives you an array of track buses).
- Use "Bus to Vector" to flatten each track bus into a vector of fields.
- Finally you can use a "Math Function" block to compute the Euclidean distance for each [x y] pair.
- Use the "Relational Operator" to compare the distance vector against your stopping threshold.
- Finally you can use the "Stop Simulation" block which halts the simulation to simulate an emergency stop when the comparator outputs true.