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Track library

Track description

Every track in the library is defined by a JSON file with the following fields:

  • metadata : a dictionary of key-value pairs with general information on the file content. Required fields: id, a unique identifier of the track that should contain only letters, numbers and underscores, and library version for compatibility reasons. Optional fields: description, created by and license.

  • altitude: altitude at beginning of track. This field is optional and may be used in combination with the gradients to plot the altitude profile of the complete track.

  • stops: a list of positions where stops are located. The first element of the list must be the 0 position and the remaining positions should follow a strictly increasing order. The last element of the list indicates the length of the track S. Optimized trajectories may be derived from any departure point to any destination point in the list.

  • speed limits: a list of pairs - position, speed limit - indicating the beginnings of track sections and their respective velocity restrictions. The positions must be strictly increasing and every speed limit should be different than its predecessor (otherwise there would be no need to add this pair in the list). The position of the first pair should be 0 and the position of the last pair must be smaller than the length of the track.

  • gradients: a list of pairs - position, gradient - indicating the beginnings of track sections and their respective (approximately constant) slope. The positions must be strictly increasing and every gradient should be different than its predecessor. Positive and negative gradient values indicate uphill and downhill sections respectively. The position of the first pair should be 0 and the position of the last pair must be smaller than the length of the track. The field can be omitted for level tracks.

  • curvatures: a list of triples - position, radius at start, and radius at end - indicating the beginnings of track sections and the corresponding curvature specifications. Note that the curvature of the track at a point is the reciprocal of the (signed) radius of the osculating circle at that point. A positive radius indicates a right-hand turn while a negative radius a left-hand turn. If the radius at start is equal to the radius at end then the track section has constant curvature. For a straight track the two radii have value "infinity". Different values for radius at start and radius at end denote a track section where the curvature of the section varies linearly with the travelled distance (clothoid curve) to interpolate between the two radii values. Note that the positions must be strictly increasing. The position of the first triple should be 0 and the position of the last triple must be smaller than the length of the track. The field can be omitted for straight tracks.

Note that the positions of speed limits, gradients, and curvatures will in general not coincide and a preprocessing step to derive track sections with constant properties is necessary in the context of trajectory optimization. This representation, however, makes a clear distinction between points with a speed limit change, points with a slope change, and points with a curvature change. In this way the interpretation of track properties is simplified.

Content

  • This table summarizes the collected benchmark instances and some of their properties