Simulation/Output/SSM Device

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Revision as of 13:06, 26 July 2017 by Leo (talk | contribs) (Available SSMs)
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Equipping vehicles

A vehicle can be equipped with an SSM Device which logs the conflicts of the vehicle and other traffic participants (currently only vehicles) and corresponding safety surrogate measures. To attach an SSM device to a vehicle, the standard device-equipment procedures can be applied using <device name>=ssm.

For instance, a single vehicle can be equipped (with a device parametrized by default values) as in the following minimal example

    <vehicle id="v0" route="route0" depart="0">
        <param key="has.ssm.device" value="true"/>

The SSM device generates an output file (one for each vehicle named ssm_<vehicleID>.xml per default, but several vehicles may write to the same file). The top level elements of the generated file are

<conflict begin="<log-begin-time>" end="<log-end-time>" ego="<equipped-vehicleID>" foe="<opponent-vehicleID>"> ... </conflict>.

The detail of information given for each conflict and the criteria to qualify an encounter as a conflict (i.e., produce a corresponding conflict element in the output) can be customized by a number of generic parameters to the vehicle or device, resp.. A full parametrization (redundantly assigning the default values, here) could look as follows:

    <vehicle id="v0" route="route0" depart="0">
        <param key="has.ssm.device" value="true"/>
        <param key="device.ssm.measures" value="TTC DRAC PET"/>
        <param key="device.ssm.thresholds" value="3.0 4.0 2.0"/> 
        <param key="device.ssm.range" value="50.0" />
        <param key="device.ssm.extratime" value="5.0" />
        <param key="device.ssm.file" value="ssm_v0.xml" />
        <param key="device.ssm.trajectories" value="false" />
        <param key="device.ssm.geo value="false" />


The possible parameters are summarized in the following table

Parameter Type Default Remark
measures list of strings All available SSMs This space-separated list of SSM-identifiers determines, which SSMs are calculated for the equipped vehicle's encounters
thresholds list of floats default thresholds for specified measures This space-separated list of SSM-thresholds determines, which encounters are classified as conflicts (if their measurements exceed a threshold) and thus written to the output file as a <conflict>-element. The thresholds for the available SSMs are: TTC<3.0[s], DRAC>4.0[m/s^2], PET<2.0[s]. This list is required to have the same length as the list of measures if given.
range double 50.0 [m] The devices detection range in meters. Other vehicles are tracked as soon as the are closer than <range> to the the equipped vehicle along the road-network. A tree search is performed to find all vehicles up to range upstream and downstream to the vehicle's current position. Further, for all downstream junctions in range, an upstream search for the given range is performed.
extratime double 5.0 [s] The extra time that an encounter is tracked on after not being associated to a potential conflict (either after crossing the conflict area, deviating from a common route, changing lanes, or because vehicles leave the device range, etc.).
file string "ssm_<equipped_vehicleID>.xml" The filename for storing the conflict information of the equipped vehicle. Several vehicles may write to the same file. Conflicts of a single vehicle are written in the order of the log-begin of the encounter.
trajectories bool false Whether the full time lines of the different measured values shall be written to the output. This includes logging the time values, encounter types, vehicle positions and velocities, values of the selected SSMs, and associated conflict point locations. If turned off (default) only the extremal values for the selected SSMs are written.
geo bool false Whether the positions in the output file shall be given in the original coordinate reference system of the network (if available).
Under development.

Encounter types

Different types of encounters, e.g. crossing, merging, or lead/follow situations, may imply different calculation procedures for the safety measures. Therefore the SSM-device keeps track of these classifications and provides them in the output to allow the correct interpretation of the corresponding values.

Currently the encounter classification is only provided when turning on the option trajectories, e.g. putting <param key="device.ssm.trajectories" value="true"/> into the configuration file.

TODO: provide map of encounter type codes

Available SSMs

TODO: Specify how implemented SSMs are computed for different encounter types