osi_logicallane.proto

syntax = "proto2";

option optimize_for = SPEED;

import "osi_common.proto";

package osi3;

//
// \brief Boundary line of a LogicalLane
//
// Similar to a LaneBoundary, but with a reference line and ST positions.
//
// A logical lane boundary describes the boundary between two logical lanes. As
// such, there will always be exactly one logical lane boundary between two
// lanes at a given S position. Contrary to that, there can be 0 to N physical
// lane boundaries (i.e. type LaneBoundary) between two logical lanes at a
// given S position.
//
// If there are multiple physical lane boundaries at one S position between two
// lanes (think of a solid-broken marking, which would be described by two
// LaneBoundary objects, one for the solid lane marking, one for the broken lane
// marking), then the single LogicalLaneBoundary describing the boundary between
// two logical lanes should be between the physical boundaries.
//
// A logical lane boundary consists of a list of \link LogicalBoundaryPoint
// LogicalBoundaryPoints\endlink. Each point has a XYZ and an ST coordinate.
// The XYZ coordinates describe the position and height of the boundary in the
// world.
//
// Notes on design decisions:
// - The LogicalLaneBoundary has ST coordinates, and is thus a separate type
//   from LaneBoundary.
//   Advantages of this decision:
//   - Calculations like getting the lane width at a position are easy, since
//     one can just get the boundary points of the left and right boundary at
//     the desired S position (via linear interpolation), and calculate the
//     width from the two points. Also getting something like the distance to
//     the lane border is very easy.
//   - No centerline of the lane is necessary, since this can very easily be
//     generated from the boundaries.
//   Disadvantages of this decision:
//   - %Lane boundaries cannot be shared with physical lanes. This results in
//     more data needed. This can mostly be mitigated by only transmitting the
//     lane boundaries during initialization (e.g. via the OSMP GroundTruthInit
//     message).
// - The LogicalLaneBoundary contains all data directly which an agent model is
//   likely to need. It does not include information normally only used by
//   sensor models (e.g. the exact length of the color markings on the road).
//   This information can be gotten from the physical lane referenced in the
//   LogicalLane, if needed.
//
message LogicalLaneBoundary
{
    // The ID of the lane boundary.
    //
    // \rules
    // is_globally_unique
    // \endrules
    //
    optional Identifier id = 1;

    // Points making up the lane boundary.
    //
    // The boundary must be defined in the same direction as the reference
    // line. So S positions should increase along the line. Note that S
    // positions will not always increase strictly monotonically.
    // Example:
    // <pre>
    //                |---------\
    //                |          \
    //  /---boundary--|           \\------------
    // /
    // ---------- reference line --------------
    // </pre>
    // At the place where the boundary suddenly increases, two points will have
    // the same S coordinate.
    //
    // If the boundary approximates a curve (e.g. a cubic function in
    // OpenDRIVE), the points must be chosen in a way that the lateral distance
    // to the ideal line does not exceed 5cm. As shown in the following image:
    //
    // \image html line_approximation_error.svg "Approximation error"
    // Approximation error green line.
    //
    // The Z error (difference in Z height between #boundary_line and the
    // "real" line) must not exceed 2cm. This is a stricter requirement than
    // for errors in the XY plane, because Z differences between lanes
    // influence driving very much.
    //
    // Note: if two lanes have different Z heights (e.g. a driving lane is
    // beside a sidewalk, where the sidewalk is 10cm higher than the road),
    // then these lanes cannot share a boundary, since their boundaries have
    // different Z heights.
    //
    repeated LogicalBoundaryPoint boundary_line = 2;

    // The reference line for this boundary.
    //
    // The reference line is used as a coordinate system for this boundary.
    // All points of this LogicalLaneBoundary must have S coordinates in the
    // range [\c sStart,\c sEnd].
    //
    // The reference line should roughly have the same shape as the boundary (so
    // roughly parallel to the lane middle), so that S coordinates continually
    // increase along the boundary.
    //
    // \rules
    // refers_to: ReferenceLine
    // \endrules
    //
    optional Identifier reference_line_id = 3;

    // Reference to the physical lane boundary or boundaries that make up this
    // logical boundary.
    //
    // Rules and notes:
    // - This list is empty if there are no physical lane boundaries to delimit
    //   a lane.
    // - In the common case, this will contain one physical boundary.
    // - This list contains several lane boundaries if there are several physical
    //   lane boundaries at one S position (e.g. both a broken and a solid
    //   line).
    // - If there are several lane boundaries, they must be listed in increasing
    //   T order (i.e. from right to left in reference line direction).
    //   Rationale: this makes it easier to determine e.g. rules on lane
    //   changes, which depend on the T order of the lanes.
    // - Whenever physical lane boundaries begin or end, or switch their T
    //   position (if there are multiple physical lane boundaries), a new
    //   LogicalLaneBoundary must be created.
    // - The referenced LaneBoundary objects may be longer than the
    //   LogicalLaneBoundary which references them, but must never be shorter.
    //
    // Example:
    // <pre>
    //       Lane 1
    //  --------a------------------ - - - -c- - - -           ----&gt;
    //  \- - - -b- - - -
    //       Lane -1
    // </pre>
    //
    // This shows the boundary between lane 1 and lane -1, with the reference
    // line going from left to right. First there is a solid-broken line (a and
    // b), then there is only a solid line (a), then there is a broken line
    // (c). There would be three LogicalLaneBoundary objects between Lane1 and
    // Lane2: the first would reference first b and then a, the second would
    // reference only a, and the third would reference c.
    //
    // \rules
    // refers_to: LaneBoundary
    // \endrules
    //
    repeated Identifier physical_boundary_id = 4;

    // The passing rules, insomuch as they can be determined just from road
    // markings.
    //
    optional PassingRule passing_rule = 5;

    // Optional external reference to the lane boundary source.
    //
    // \note For OpenDRIVE, there is no direct possibility to reference the
    //       RoadMark, as there is no unique identifier in this sub-object.
    //
    // \note For non-ASAM Standards, it is implementation-specific how
    //       source_reference is resolved.
    //
    // \note The value has to be repeated because one object may be derived
    //       from more than one origin source, for example, from a scenario file
    //       and from sensors.
    //
    repeated ExternalReference source_reference = 6;

    //
    // \brief A point on the boundary
    //
    message LogicalBoundaryPoint
    {

        // The position of the \c LaneBoundaryPoint.
        //
        optional Vector3d position = 1;

        // S position of the LaneBoundaryPoint, measured along the parent's
        // reference_line_id.
        //
        optional double s_position = 2;

        // T position of the LaneBoundaryPoint, measured along the parent's
        // reference_line_id.
        //
        optional double t_position = 3;
    }

    //
    // Passing rule of the LogicalLaneBoundary.
    //
    // This describes how vehicles may move across the LogicalLaneBoundary. The
    // PassingRule is determined solely based on the road, not on any signs
    // (i.e. it may be overridden by signs).
    //
    enum PassingRule
    {
        // Passing rule is unknown (must not be used in ground truth).
        //
        PASSING_RULE_UNKNOWN = 0;

        // Passing rule fits neither of the other categories.
        //
        // Example: this type needs to be used if passing depends on the agent
        // type, e.g. if cars may change lane, but trucks may not.
        //
        // This value is also used between non-drivable lanes where the traffic
        // regulations do not say anything about passing rules (e.g. for a lane
        // boundary between lanes of TYPE_BORDER and TYPE_SHOULDER).
        //
        PASSING_RULE_OTHER = 1;

        // No passing is allowed (neither from left to right nor from right to
        // left).
        //
        PASSING_RULE_NONE_ALLOWED = 2;

        // Only passing in increasing T direction allowed. Passing is allowed
        // from one lane to the other if the points on the target lane have
        // larger T values than points on the source lane (at the same S
        // position). In reference line direction (but not necessarily in
        // driving direction), this means changing from right to left is
        // allowed.
        //
        PASSING_RULE_INCREASING_T = 3;

        // Only passing in decreasing T direction allowed. Passing is allowed
        // from one lane to the other if the points on the target lane have
        // smaller T values than points on the source lane (at the same S
        // position). In reference line direction (but not necessarily in
        // driving direction), this means changing from left to right is
        // allowed.
        //
        PASSING_RULE_DECREASING_T = 4;

        // Passing is allowed in both directions (left to right and right to
        // left).
        //
        PASSING_RULE_BOTH_ALLOWED = 5;
    }
}

//
// \brief A logical lane in the road network.
//
// A logical lane is part of a road. Compared to a physical lane (OSI type
// \c Lane), its existence doesn't hinge on the existence of road markings. So
// e.g. a road with two driving directions but no road markings in-between
// would be presented as two \link LogicalLane LogicalLanes\endlink, but only
// one Lane. So one Lane can consist of multiple \link LogicalLane
// LogicalLanes\endlink. E.g. on intersections, each driving path is one
// LogicalLane, but the whole area is one \c Lane of type \link
// osi3::Lane::Classification::TYPE_INTERSECTION \c TYPE_INTERSECTION \endlink.
//
// Outside of intersections, logical lanes are constructed such that each point on
// the road belongs to at least one (typically: exactly one) logical lane. So
// there are no gaps between logical lanes, and no areas that don't belong to a
// logical lane.
//
// If OSI is generated from OpenDRIVE, then \link LogicalLane
// LogicalLanes\endlink map directly to OpenDRIVE lanes. However, it is allowed
// to merge multiple consecutive (in S direction) OpenDRIVE lanes with the same
// type into one OSI LogicalLane: if an OpenDRIVE lane has a single successor,
// which has the same lane type, and this successor has only one predecessor
// (so no lane merging or splitting) then the two lanes may be presented as one
// continuous LogicalLane. This may be done recursively.
//
// The \link ReferenceLine reference line\endlink pointed to by
// #reference_line_id defines an ST coordinate system for the lane. This ST
// coordinate system is used to describe positions on the lane.
//
// ## Example
//
// The example below shows two logical lanes on an intersection, with a focus
// on the left-turn lane (\c l1):
// \image html OSI_LogicalLane1.png "Two logical lanes on an intersection"
//
// Assumptions not shown in the image:
// - This is right-hand traffic (and thus vehicles on \c l1 drive from the bottom
//   to the left, vehicles on \c l2 drive from right to left).
// - The yellow line is a ReferenceLine, defined starting at the bottom, and
//   going to the left.
//
// Some features shown in the image relative to \c l1:
// - The yellow line is the ReferenceLine of \c l1 . The ReferenceLine can be
//   shared with other lanes.  Because the ReferenceLine has the same direction
//   as the driving direction of \c l1 in this example,
//   <code>#move_direction == #MOVE_DIRECTION_INCREASING_S</code>.
// - The red line marks the area where \c l2 is left of
//   \c l1 - this info is recorded in #left_adjacent_lane of \c l1.
// - The red area is the area where \c l2 overlaps \c l1. This is recorded in
//   #overlapping_lane of \c l1.
//
// The image below shows the same two lanes, but from the perspective of \c l2:
// \image html OSI_LogicalLane2.png "Two logical lanes on an intersection"
//
// Assumptions not shown in the image:
// - The yellow line is a ReferenceLine, defined starting at the right, going
//   to the left.
//
// Some features shown in the image relative to \c l2:
// - The yellow line is the ReferenceLine of \c l2 . The ReferenceLine can be
//   shared with other lanes.  Because the ReferenceLine has the same direction
//   as the driving direction of \c l2 in this example,
//   <code>#move_direction == #MOVE_DIRECTION_INCREASING_S</code>.
// - The green line marks the area where \c l1 is right of
//   \c l2 - this info is recorded in #right_adjacent_lane of \c l2.
// - The red area is the area where \c l1 overlaps \c l2. This is recorded in
//   #overlapping_lane of \c l1.
//
// As can be seen in the images, the two highlighted lanes are neighbours for
// part of their length, but it makes no sense for them to have the same
// reference line, since they diverge significantly.
//
// Note: all the relations shown above are also defined outside of intersections.
//
message LogicalLane
{
    // The ID of the logical lane.
    //
    // \note Note ID is global unique.
    //
    // \rules
    // is_globally_unique
    // \endrules
    //
    optional Identifier id = 1;

    // The type of the logical lane.
    //
    optional Type type = 2;

    // Optional external reference to the lane source.
    //
    // The external reference points to the source of the lane, if it is derived
    // from one or more objects or external references.
    //
    // For example, to reference a lane defined in an OpenDRIVE map
    // the items should be set as follows:
    // * reference = URI to map, can remain empty if identical with definiton
    //               in \c GroundTruth::map_reference
    // * type = "net.asam.opendrive"
    // * identifier[0] = id of t_road
    // * identifier[1] = s of t_road_lanes_laneSection
    // * identifier[2] = id of t_road_lanes_laneSection_left_lane,
    //                         t_road_lanes_laneSection_right_lane
    //
    // \note For non-ASAM Standards, it is implementation-specific how
    //       source_reference is resolved.
    //
    // \note The value has to be repeated, because one lane segment may be
    //       derived from more than one origin segment. Multiple sources
    //       may be added as reference as well, for example, a map and sensors.
    //
    repeated ExternalReference source_reference = 3;

    // Reference to the physical lanes this logical lane belongs to.
    //
    // This makes it possible to get detailed information on the physical lane
    // properties, e.g. the visual colors of the boundaries, the road
    // condition, etc..
    //
    // Note: a logical lane may consist of several physical lanes (in a row).
    // At any one S position, a logical lane should only reference one physical
    // lane. Several logical lanes may reference the same physical lane (see
    // drawing below).
    //
    // Logical lanes should not extend beyond intersections. All logical lanes
    // on intersections should end at the latest at the border of the
    // intersection.
    //
    // Example:
    // <pre>
    // ---------------------------------
    //  l1                       l2
    // ----------    l3        ---------
    //  l4                       l5
    // ---------------------------------
    // </pre>
    //
    // In this case, we have five physical lanes: l1, l2, l4 and l5 where a
    // lane marking is present. And l3 is one lane covering the whole road
    // (because no road marking is present).
    //
    // This would typically be presented as two logical lanes:
    // - One encompassing l1, part of l3, and l2
    // - The other encompassing l4, part of l3 and l5
    //
    // In this example, both logical lanes would reference l3. Their shared
    // LogicalLaneBoundary would cut through the middle of l3.
    //
    // physical_lane_reference does not give any information how much of the
    // area of a physical lane is covered by a logical lane.
    //
    // \rules
    // refers_to: Lane
    // \endrules
    //
    repeated PhysicalLaneReference physical_lane_reference = 4;

    // The \link ReferenceLine reference line\endlink for this logical lane
    //
    // The reference line is used as a coordinate system on this lane.
    //
    // The reference line should roughly have the same shape as the lane, so
    // that S coordinates continually increase/decrease along the lane. It is
    // not required that the reference line has the same direction as the
    // driving direction of the lane.
    //
    // Neighbouring lanes (i.e. lanes that are neighbours and whose directions
    // do not diverge significantly) are strongly encouraged to reference the
    // same ReferenceLine, so that vehicles that are next to each other on
    // neighbouring lanes have comparable S positions.
    //
    // The S coordinate of the reference line makes it easy to find e.g. which
    // object is next on a lane, using the LogicalLaneAssignment of the
    // objects.
    //
    // The reference trajectory must be sampled such that there are no two
    // positions on the lane more than 5cm apart with the same ST coordinate.
    //
    // \rules
    // refers_to: ReferenceLine
    // \endrules
    //
    optional Identifier reference_line_id = 5;

    // Start S position of the lane.
    //
    // Must be in range [\c sStart,\c sEnd] of the reference line.
    //
    optional double start_s = 6;

    // End S position of the lane.
    //
    // Must be in range [\c sStart,\c sEnd] of the reference line.
    //
    // Requirement: #end_s > #start_s
    //
    optional double end_s = 7;

    // Definition of the intended driving direction.
    //
    optional MoveDirection move_direction = 8;

    // Lanes that are directly right of this lane, without gap or overlap.
    //
    // "Right" is in definition direction (not driving direction), so right lanes
    // have smaller T coordinates.
    // Entries must be ordered: first by #start_s, then by #end_s.
    //
    // The XY positions of the polyline generated by the LogicalLaneBoundaries
    // of adjacent lanes must match up to a small error (5cm).
    // Typically adjacent lanes will share a LogicalLaneBoundary, but this will
    // not always be true. Examples: on intersections, it might be hard to generate
    // data such that lanes that are adjacent for a short length share a
    // LogicalLaneBoundary for this length; also different LogicalLaneBoundaries
    // are needed if the lanes have different heights at their boundaries (e.g.
    // road adjacent to a sidewalk).
    //
    repeated LaneRelation right_adjacent_lane = 9;

    // Lanes that are directly left of this lane, without gap or overlap.
    //
    // "Left" is in definition direction (not driving direction), so left lanes
    // have larger T coordinates.
    // Entries must be ordered: first by #start_s, then by #end_s.
    //
    // The XY positions of the polyline generated by the LogicalLaneBoundaries
    // of adjacent lanes must match up to a small error (5cm).
    // Typically adjacent lanes will share a LogicalLaneBoundary, but this will
    // not always be true. Examples: on intersections, it might be hard to generate
    // data such that lanes that are adjacent for a short length share a
    // LogicalLaneBoundary for this length; also different LogicalLaneBoundaries
    // are needed if the lanes have different heights at their boundaries (e.g.
    // road adjacent to a sidewalk).
    //
    repeated LaneRelation left_adjacent_lane = 10;

    // Lanes that partially or completely overlap this lane.
    //
    // Only overlaps laterally larger than 5cm are considered overlaps for the
    // purpose of this relation.
    //
    // This will typically contain a lot of entries on intersections, but might
    // also be used outside of intersections (e.g. if a #TYPE_BIKING lane
    // overlaps a #TYPE_NORMAL lane).
    //
    // Entries must be ordered: first by #start_s, then by #end_s.
    //
    repeated LaneRelation overlapping_lane = 11;

    // Right boundary of this lane.
    //
    // References to LogicalLaneBoundary elements.
    // All LogicalLaneBoundary elements referenced here must refer to the same
    // ReferenceLine as this lane.
    // The boundaries together must cover the whole length of the lane (the
    // range \[#start_s,#end_s\]) without gap or overlap. The boundaries must be
    // stored in ascending order, starting with the smallest S position.
    // Consecutive boundaries must share a point: the last point of the
    // previous boundary must be identical to the first point of the next
    // boundary.
    //
    // Note: the referenced boundaries may have points outside of
    // \[#start_s,#end_s\] (e.g. a boundary may extend beyond the end of a lane).
    //
    // \rules
    // refers_to: LogicalLaneBoundary
    // \endrules
    //
    repeated Identifier right_boundary_id = 12;

    // Left boundary of this lane.
    //
    // References to LogicalLaneBoundary elements.
    // All LogicalLaneBoundary elements referenced here must refer to the same
    // ReferenceLine as this lane.
    // The boundaries together must cover the whole length of the lane (the
    // range \[#start_s,#end_s\]) without gap or overlap. The boundaries must be
    // stored in ascending order, starting with the smallest S position.
    // Consecutive boundaries must share a point: the last point of the
    // previous boundary must be identical to the first point of the next
    // boundary.
    //
    // Note: the referenced boundaries may have points outside of
    // \[#start_s,#end_s\] (e.g. a boundary may extend beyond the end of a lane).
    //
    // \rules
    // refers_to: LogicalLaneBoundary
    // \endrules
    //
    repeated Identifier left_boundary_id = 13;

    // Lanes that directly are connected to this lane at the beginning.
    //
    // "Beginning" is relative to the reference line, so connections at #start_s.
    //
    // Lane predecessors and successors shall only be used to connect lanes if
    // a physical connection at the beginning or end of both lanes exist. Both
    // lanes have a non-zero width at the connection point and they are
    // semantically connected.
    //
    // A lane may have several predecessors e.g. on intersections, or if a wide
    // lane splits into two, or two merge into one.
    //
    repeated LaneConnection predecessor_lane = 14;

    // Lanes that directly are connected to this lane at the end.
    //
    // "End" is relative to the reference line, so connections at #end_s.
    //
    // Lane predecessors and successors shall only be used to connect lanes if
    // a physical connection at the beginning or end of both lanes exist. Both
    // lanes have a non-zero width at the connection point and they are
    // semantically connected.
    //
    // A lane may have several successors e.g. on intersections, or if a wide
    // lane splits into two, or two merge into one.
    //
    repeated LaneConnection successor_lane = 15;

    //
    // Definition of available lane types.
    //
    // This is mostly aligned with OpenDRIVE, except that lane types modelling
    // access restrictions (e.g. "taxi") are not made available here. These are
    // already deprecated in OpenDRIVE.  To support this, access restrictions
    // should be added later, in alignment with OpenDRIVE.
    //
    enum Type
    {
        // %Lane of unknown type. Do not use in ground truth.
        //
        TYPE_UNKNOWN = 0;

        // Any other type of lane.
        //
        TYPE_OTHER = 1;

        // A normal driving lane.
        // Example: Lanes with IDs l1, l2, l3 and l4 in image \ref
        // HighwayExit.
        // This matches the OpenDRIVE type "driving".
        //
        // Note: a lane with OpenDRIVE type "bidirectional" will have an OSI
        // type of TYPE_NORMAL, with <code>#move_direction ==
        // #MOVE_DIRECTION_BOTH_ALLOWED</code>.
        //
        TYPE_NORMAL = 2;

        // A lane that is designated for bicylists.
        // Note that biking lanes that cross the road (e.g. on an intersection)
        // are also labeled with this type.
        //
        TYPE_BIKING = 3;

        // A lane that is designated for pedestrians (sidewalk).
        // Note that pedestrian lanes that cross the road (e.g. on an
        // intersection) are also labeled with this type.
        //
        TYPE_SIDEWALK = 4;

        // A lane with parking spaces.
        //
        TYPE_PARKING = 5;

        // A hard shoulder on motorways for emergency stops.
        // Example: Lane l5 in image \ref
        // HighwayExit.
        //
        TYPE_STOP = 6;

        // A lane on which cars should not drive.
        //
        TYPE_RESTRICTED = 7;

        // A hard border on the edge of a road.
        //
        TYPE_BORDER = 8;

        // A soft border on the edge of a road.
        //
        TYPE_SHOULDER = 9;

        // A deceleration lane in parallel to the main road.
        // Example: Lane l6 in image \ref
        // HighwayExit.
        //
        TYPE_EXIT = 10;

        // An acceleration lane in parallel to the main road.
        //
        TYPE_ENTRY = 11;

        // A ramp from rural or urban roads joining a motorway.
        //
        TYPE_ONRAMP = 12;

        // A ramp leading off a motorway onto rural or urban roads.
        //
        TYPE_OFFRAMP = 13;

        // A ramp that connect two motorways.
        //
        TYPE_CONNECTINGRAMP = 14;

        // A lane that sits between driving lanes
        // that lead in opposite directions. It is
        // typically used to separate traffic in
        // towns on large roads.
        //
        TYPE_MEDIAN = 15;

        // Curb stones. Curb stones have a different
        // height than the adjacent drivable lanes.
        //
        TYPE_CURB = 16;

        // A rail lane. This lane covers the area a train needs to drive along
        // its rails.
        // #overlapping_lane then describes where a train crosses other lanes.
        //
        TYPE_RAIL = 17;

        // A tram lane. This lane covers the area a tram needs to drive along
        // its rails.
        // #overlapping_lane then describes where a tram crosses other lanes.
        //
        TYPE_TRAM = 18;
    }

    //
    // \brief Reference to a physical lane.
    //
    message PhysicalLaneReference
    {
        // Id of the physical lane referenced.
        //
        // \rules
        // refers_to: Lane
        // \endrules
        //
        optional Identifier physical_lane_id = 1;

        // S position on the logical lane where the physical lane starts.
        //
        optional double start_s = 2;

        // S position on the logical lane where the physical lane ends.
        //
        // Requirement: #end_s > #start_s
        //
        optional double end_s = 3;
    }

    //
    // Describes in which direction moving objects may typically move along a
    // lane.
    //
    // This describes the allowed typical driving direction on a lane, or (in
    // the case of pedestrian) the allowed walking direction.
    //
    // Note: Allowed overtaking (e.g. on country roads) does not automatically
    // make a lane bidirectional, since vehicles may normally only drive in the
    // other direction during the overtake maneuver, not for longer periods of
    // time.
    //
    enum MoveDirection
    {
        // Move direction is unknown. Do not use in ground truth.
        //
        MOVE_DIRECTION_UNKNOWN = 0;

        // Move direction fits neither of the other categories.
        //
        // Example: a lane where cars may only drive in one direction, but
        // bikes may drive in both.
        //
        MOVE_DIRECTION_OTHER = 1;

        // Objects may move in increasing S direction.
        //
        // This means they move in the same direction as the reference line.
        //
        MOVE_DIRECTION_INCREASING_S = 2;

        // Objects may move in decreasing S direction.
        //
        // This means they move in the opposite direction as the reference line.
        //
        MOVE_DIRECTION_DECREASING_S = 3;

        // Objects may move in both directions.
        //
        MOVE_DIRECTION_BOTH_ALLOWED = 4;
    }

    //
    // \brief Connection to another lane (predecessor or successor)
    //
    message LaneConnection
    {
        // Id of the other logical lane that is connected.
        //
        // \rules
        // refers_to: LogicalLane
        // \endrules
        //
        optional Identifier other_lane_id = 1;

        // If true: LaneConnection is at the beginning of the other lane
        // If false: LaneConnection is a the end of the other lane
        //
        optional bool at_begin_of_other_lane = 2;

    }

    //
    // \brief Relation of this lane to another logical lane
    //
    message LaneRelation
    {
        // Id of the other logical lane.
        //
        // \rules
        // refers_to: LogicalLane
        // \endrules
        //
        optional Identifier other_lane_id = 1;

        // Start s position of the relation.
        //
        optional double start_s = 2;

        // End s position of the relation.
        //
        // Requirement: #end_s > #start_s
        //
        optional double end_s = 3;

        // Start s position of the relation on the other lane.
        //
        // This is the same place as #start_s, but measured along the reference
        // line of the other lane.
        //
        optional double start_s_other = 4;

        // End s position of the relation on the other lane.
        //
        // This is the same place as #end_s, but measured along the reference
        // line of the other lane.
        //
        // Note: #end_s_other might be smaller than #start_s_other
        //
        optional double end_s_other = 5;
    }
}