For What Locations Does INRIX TPEG Return Data?
When TPEG data is returned to a vehicle, it contains information only for locations that are expected to be relevant to the vehicle. There are two types of scenarios that are covered:
- Unguided Scenarios. No destination is specified. Only location and heading are specified.
- Guided Scenarios. A destination is specified.
When you request data with the message call, you specify whether you want data for a guided or unguided scenario. Data is returned in a series of circles. For unguided scenarios, TPEG data is returned for three concentric circles centered at the vehicle’s location. For guided scenarios where a destination is specified, TPEG data is provided for the three circles as well as an additional circle centered at the destination, as well as the most likely routes between current location and destination. The radii of the circles can be specified when the session is initialized. If they are not specified, then default values will be used. The default values are described in the next section. Note: By specifying the radius values, you can affect the size of the data returned. If bandwidth is an issue, choosing smaller radii will reduce the amount of data. If it is not, you may choose larger radii in order to obtain more data to display.
Traffic flow and incident (TFP and TEC) data are returned for three concentric circles with the most data returned for the circle with the smallest radius, and less data returned for the larger circles, and shown in the image below. The size of each radius can be specified in the session call, or else the default values are used.
The following table describes the locations for which data is returned, as well as the default radii. See the FRC glossary entry for an explanation of how the FRC values indicate road class. Note that a TEC closure is an incident that results in a road closure.
|Circle or Ring||TPEG Data Locations Returned||Default Radius|
TMCs are often grouped into a “linears”, which are TMCs that are connected together. If any TMC in a linear is located within a circle and TPEG data is returned for that TMC, then TPEG data may be returned for all TMCs in that linear. In order for data to be returned for TMCs outside of the circle, the linear must be going in the direction of inside of the circle towards outside of the circle.
Guided scenarios work almost exactly like unguided scenarios, but some additional data is returned:
- A circle identical to the inner circle is applied to the destination location. This circle has the same radius and returns data for the same FRC levels as the inner circle around the vehicle.
- Data is returned for the routes that the vehicle is most likely to take to the destination. Data for up to three routes is returned.
The following picture illustrates the circles and routes of a guided scenario:
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