google Transit APIs 谷歌实时交通数据接口GTFS（三） 数据结构

GTFS实时提要使运输公司可以为消费者提供有关其车辆位置（车站关闭，线路无法运行，重要的延误等）服务中断以及预计到达时间的实时信息。Feed规范的2.0版。

定义需要在GTFS-realtime v2.0和更高版本中，“必填”列描述了生产者必须提供哪些字段，以便传输数据有效并对使用中的应用程序有意义。

在“必需”字段中使用以下值：

必填：此字段必须由GTFS实时供稿生成者提供。
有条件地要求：在某些条件下，此字段是必需的，这些条件在“说明”字段中概述。在这些条件之外，该字段是可选的。
可选：此字段是可选的，生产者不需要实施。但是，如果底层自动车辆定位系统中有可用数据（例如VehiclePosition时间戳），则建议生产者在可能的情况下提供这些可选字段。
请注意，GTFS-realtime版本1.0中未定义语义要求，因此gtfs_realtime_version为1的供稿可能无法满足这些要求（有关详细信息，请参阅建议书）。

基数表示可以为特定字段提供的元素数，具有以下值：

一个-可以为此字段提供一个单个元素。 这映射到必需的协议缓冲区和可选基数。
可以为该字段提供很多-许多元素（0、1或更多）。 这映射到协议缓冲区重复基数。
始终引用“必填”和“描述”字段以查看何时需要，有条件必填或可选字段。

协议缓冲区数据类型
以下协议缓冲区数据类型用于描述提要元素：

消息：复杂类型
枚举：固定值列表

FeedMessage
FeedHeader
增量性
FeedEntity
TripUpdate
TripDescriptor
时间表关系
车辆描述符
StopTime更新
StopTimeEvent
时间表关系
车辆位置
TripDescriptor
时间表关系
车辆描述符
位置
车辆停止状态
拥塞水平
占用状态
警报
时间范围
实体选择器
TripDescriptor
时间表关系
原因
影响
翻译字符串
翻译

 

消息FeedEntity
运输提要中实体的定义（或更新）。如果未删除实体，则应填写“ trip_update”，“ vehicle”和“ alert”字段之一。

领域
字段名称类型必需基数描述
id字符串此实体的一个Feed唯一标识符。这些ID仅用于提供增量支持。提要引用的实际实体必须由显式选择器指定（有关更多信息，请参见下面的EntitySelector）。
is_deleted bool可选一个是否要删除此实体。仅应为增量为DIFFERENTIAL的供稿提供-不应为增量为FULL_DATASET的供稿提供此字段。
trip_update TripUpdate有条件地需要一个有关行程的实时出发延误的数据。必须至少提供Trip_update，vehicle或alert字段之一-所有这些字段都不能为空。
vehicle VehiclePosition有条件地需要一个有关车辆实时位置的数据。必须至少提供Trip_update，vehicle或alert字段之一-所有这些字段都不能为空。
警报警报有条件地需要一个有关实时警报的数据。必须至少提供Trip_update，vehicle或alert字段之一-所有这些字段都不能为空。

 

 

// Copyright 2015 The GTFS Specifications Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Protocol definition file for GTFS Realtime.
//
// GTFS Realtime lets transit agencies provide consumers with realtime
// information about disruptions to their service (stations closed, lines not
// operating, important delays etc), location of their vehicles and expected
// arrival times.
//
// This protocol is published at:
// https://github.com/google/transit/tree/master/gtfs-realtime

syntax = "proto2";

package transit_realtime;

option java_package = "com.google.transit.realtime";

// The contents of a feed message.
// A feed is a continuous stream of feed messages. Each message in the stream is
// obtained as a response to an appropriate HTTP GET request.
// A realtime feed is always defined with relation to an existing GTFS feed.
// All the entity ids are resolved with respect to the GTFS feed.
// Note that "required" and "optional" as stated in this file refer to Protocol
// Buffer cardinality, not semantic cardinality.  See reference.md at
// https://github.com/google/transit/tree/master/gtfs-realtime for field
// semantic cardinality.
message FeedMessage {
  // Metadata about this feed and feed message.
  required FeedHeader header = 1;

  // Contents of the feed.
  repeated FeedEntity entity = 2;

  // The extensions namespace allows 3rd-party developers to extend the
  // GTFS Realtime specification in order to add and evaluate new features and
  // modifications to the spec.
  extensions 1000 to 1999;
}

// Metadata about a feed, included in feed messages.
message FeedHeader {
  // Version of the feed specification.
  // The current version is 2.0.
  required string gtfs_realtime_version = 1;

  // Determines whether the current fetch is incremental.  Currently,
  // DIFFERENTIAL mode is unsupported and behavior is unspecified for feeds
  // that use this mode.  There are discussions on the GTFS Realtime mailing
  // list around fully specifying the behavior of DIFFERENTIAL mode and the
  // documentation will be updated when those discussions are finalized.
  enum Incrementality {
    FULL_DATASET = 0;
    DIFFERENTIAL = 1;
  }
  optional Incrementality incrementality = 2 [default = FULL_DATASET];

  // This timestamp identifies the moment when the content of this feed has been
  // created (in server time). In POSIX time (i.e., number of seconds since
  // January 1st 1970 00:00:00 UTC).
  optional uint64 timestamp = 3;

  // The extensions namespace allows 3rd-party developers to extend the
  // GTFS Realtime specification in order to add and evaluate new features and
  // modifications to the spec.
  extensions 1000 to 1999;
}

// A definition (or update) of an entity in the transit feed.
message FeedEntity {
  // The ids are used only to provide incrementality support. The id should be
  // unique within a FeedMessage. Consequent FeedMessages may contain
  // FeedEntities with the same id. In case of a DIFFERENTIAL update the new
  // FeedEntity with some id will replace the old FeedEntity with the same id
  // (or delete it - see is_deleted below).
  // The actual GTFS entities (e.g. stations, routes, trips) referenced by the
  // feed must be specified by explicit selectors (see EntitySelector below for
  // more info).
  required string id = 1;

  // Whether this entity is to be deleted. Relevant only for incremental
  // fetches.
  optional bool is_deleted = 2 [default = false];

  // Data about the entity itself. Exactly one of the following fields must be
  // present (unless the entity is being deleted).
  optional TripUpdate trip_update = 3;
  optional VehiclePosition vehicle = 4;
  optional Alert alert = 5;

  // The extensions namespace allows 3rd-party developers to extend the
  // GTFS Realtime Specification in order to add and evaluate new features and
  // modifications to the spec.
  extensions 1000 to 1999;
}

//
// Entities used in the feed.
//

// Realtime update of the progress of a vehicle along a trip.
// Depending on the value of ScheduleRelationship, a TripUpdate can specify:
// - A trip that proceeds along the schedule.
// - A trip that proceeds along a route but has no fixed schedule.
// - A trip that have been added or removed with regard to schedule.
//
// The updates can be for future, predicted arrival/departure events, or for
// past events that already occurred.
// Normally, updates should get more precise and more certain (see
// uncertainty below) as the events gets closer to current time.
// Even if that is not possible, the information for past events should be
// precise and certain. In particular, if an update points to time in the past
// but its update's uncertainty is not 0, the client should conclude that the
// update is a (wrong) prediction and that the trip has not completed yet.
//
// Note that the update can describe a trip that is already completed.
// To this end, it is enough to provide an update for the last stop of the trip.
// If the time of that is in the past, the client will conclude from that that
// the whole trip is in the past (it is possible, although inconsequential, to
// also provide updates for preceding stops).
// This option is most relevant for a trip that has completed ahead of schedule,
// but according to the schedule, the trip is still proceeding at the current
// time. Removing the updates for this trip could make the client assume
// that the trip is still proceeding.
// Note that the feed provider is allowed, but not required, to purge past
// updates - this is one case where this would be practically useful.
message TripUpdate {
  // The Trip that this message applies to. There can be at most one
  // TripUpdate entity for each actual trip instance.
  // If there is none, that means there is no prediction information available.
  // It does *not* mean that the trip is progressing according to schedule.
  required TripDescriptor trip = 1;

  // Additional information on the vehicle that is serving this trip.
  optional VehicleDescriptor vehicle = 3;

  // Timing information for a single predicted event (either arrival or
  // departure).
  // Timing consists of delay and/or estimated time, and uncertainty.
  // - delay should be used when the prediction is given relative to some
  //   existing schedule in GTFS.
  // - time should be given whether there is a predicted schedule or not. If
  //   both time and delay are specified, time will take precedence
  //   (although normally, time, if given for a scheduled trip, should be
  //   equal to scheduled time in GTFS + delay).
  //
  // Uncertainty applies equally to both time and delay.
  // The uncertainty roughly specifies the expected error in true delay (but
  // note, we don't yet define its precise statistical meaning). It's possible
  // for the uncertainty to be 0, for example for trains that are driven under
  // computer timing control.
  message StopTimeEvent {
    // Delay (in seconds) can be positive (meaning that the vehicle is late) or
    // negative (meaning that the vehicle is ahead of schedule). Delay of 0
    // means that the vehicle is exactly on time.
    optional int32 delay = 1;

    // Event as absolute time.
    // In Unix time (i.e., number of seconds since January 1st 1970 00:00:00
    // UTC).
    optional int64 time = 2;

    // If uncertainty is omitted, it is interpreted as unknown.
    // If the prediction is unknown or too uncertain, the delay (or time) field
    // should be empty. In such case, the uncertainty field is ignored.
    // To specify a completely certain prediction, set its uncertainty to 0.
    optional int32 uncertainty = 3;

    // The extensions namespace allows 3rd-party developers to extend the
    // GTFS Realtime Specification in order to add and evaluate new features
    // and modifications to the spec.
    extensions 1000 to 1999;
  }

  // Realtime update for arrival and/or departure events for a given stop on a
  // trip. Updates can be supplied for both past and future events.
  // The producer is allowed, although not required, to drop past events.
  message StopTimeUpdate {
    // The update is linked to a specific stop either through stop_sequence or
    // stop_id, so one of the fields below must necessarily be set.
    // See the documentation in TripDescriptor for more information.

    // Must be the same as in stop_times.txt in the corresponding GTFS feed.
    optional uint32 stop_sequence = 1;
    // Must be the same as in stops.txt in the corresponding GTFS feed.
    optional string stop_id = 4;

    optional StopTimeEvent arrival = 2;
    optional StopTimeEvent departure = 3;

    // The relation between this StopTime and the static schedule.
    enum ScheduleRelationship {
      // The vehicle is proceeding in accordance with its static schedule of
      // stops, although not necessarily according to the times of the schedule.
      // At least one of arrival and departure must be provided. If the schedule
      // for this stop contains both arrival and departure times then so must
      // this update.
      SCHEDULED = 0;

      // The stop is skipped, i.e., the vehicle will not stop at this stop.
      // Arrival and departure are optional.
      SKIPPED = 1;

      // No data is given for this stop. The main intention for this value is to
      // give the predictions only for part of a trip, i.e., if the last update
      // for a trip has a NO_DATA specifier, then StopTimes for the rest of the
      // stops in the trip are considered to be unspecified as well.
      // Neither arrival nor departure should be supplied.
      NO_DATA = 2;
    }
    optional ScheduleRelationship schedule_relationship = 5
        [default = SCHEDULED];

    // The extensions namespace allows 3rd-party developers to extend the
    // GTFS Realtime Specification in order to add and evaluate new features
    // and modifications to the spec.
    extensions 1000 to 1999;
  }

  // Updates to StopTimes for the trip (both future, i.e., predictions, and in
  // some cases, past ones, i.e., those that already happened).
  // The updates must be sorted by stop_sequence, and apply for all the
  // following stops of the trip up to the next specified one.
  //
  // Example 1:
  // For a trip with 20 stops, a StopTimeUpdate with arrival delay and departure
  // delay of 0 for stop_sequence of the current stop means that the trip is
  // exactly on time.
  //
  // Example 2:
  // For the same trip instance, 3 StopTimeUpdates are provided:
  // - delay of 5 min for stop_sequence 3
  // - delay of 1 min for stop_sequence 8
  // - delay of unspecified duration for stop_sequence 10
  // This will be interpreted as:
  // - stop_sequences 3,4,5,6,7 have delay of 5 min.
  // - stop_sequences 8,9 have delay of 1 min.
  // - stop_sequences 10,... have unknown delay.
  repeated StopTimeUpdate stop_time_update = 2;

  // Moment at which the vehicle's real-time progress was measured. In POSIX
  // time (i.e., the number of seconds since January 1st 1970 00:00:00 UTC).
  optional uint64 timestamp = 4;

  // The current schedule deviation for the trip.  Delay should only be
  // specified when the prediction is given relative to some existing schedule
  // in GTFS.
  //
  // Delay (in seconds) can be positive (meaning that the vehicle is late) or
  // negative (meaning that the vehicle is ahead of schedule). Delay of 0
  // means that the vehicle is exactly on time.
  //
  // Delay information in StopTimeUpdates take precedent of trip-level delay
  // information, such that trip-level delay is only propagated until the next
  // stop along the trip with a StopTimeUpdate delay value specified.
  //
  // Feed providers are strongly encouraged to provide a TripUpdate.timestamp
  // value indicating when the delay value was last updated, in order to
  // evaluate the freshness of the data.
  //
  // NOTE: This field is still experimental, and subject to change. It may be
  // formally adopted in the future.
  optional int32 delay = 5;

  // The extensions namespace allows 3rd-party developers to extend the
  // GTFS Realtime Specification in order to add and evaluate new features and
  // modifications to the spec.
  extensions 1000 to 1999;
}

// Realtime positioning information for a given vehicle.
message VehiclePosition {
  // The Trip that this vehicle is serving.
  // Can be empty or partial if the vehicle can not be identified with a given
  // trip instance.
  optional TripDescriptor trip = 1;

  // Additional information on the vehicle that is serving this trip.
  optional VehicleDescriptor vehicle = 8;

  // Current position of this vehicle.
  optional Position position = 2;

  // The stop sequence index of the current stop. The meaning of
  // current_stop_sequence (i.e., the stop that it refers to) is determined by
  // current_status.
  // If current_status is missing IN_TRANSIT_TO is assumed.
  optional uint32 current_stop_sequence = 3;
  // Identifies the current stop. The value must be the same as in stops.txt in
  // the corresponding GTFS feed.
  optional string stop_id = 7;

  enum VehicleStopStatus {
    // The vehicle is just about to arrive at the stop (on a stop
    // display, the vehicle symbol typically flashes).
    INCOMING_AT = 0;

    // The vehicle is standing at the stop.
    STOPPED_AT = 1;

    // The vehicle has departed and is in transit to the next stop.
    IN_TRANSIT_TO = 2;
  }
  // The exact status of the vehicle with respect to the current stop.
  // Ignored if current_stop_sequence is missing.
  optional VehicleStopStatus current_status = 4 [default = IN_TRANSIT_TO];

  // Moment at which the vehicle's position was measured. In POSIX time
  // (i.e., number of seconds since January 1st 1970 00:00:00 UTC).
  optional uint64 timestamp = 5;

  // Congestion level that is affecting this vehicle.
  enum CongestionLevel {
    UNKNOWN_CONGESTION_LEVEL = 0;
    RUNNING_SMOOTHLY = 1;
    STOP_AND_GO = 2;
    CONGESTION = 3;
    SEVERE_CONGESTION = 4;  // People leaving their cars.
  }
  optional CongestionLevel congestion_level = 6;

  // The degree of passenger occupancy of the vehicle. This field is still
  // experimental, and subject to change. It may be formally adopted in the
  // future.
  enum OccupancyStatus {
    // The vehicle is considered empty by most measures, and has few or no
    // passengers onboard, but is still accepting passengers.
    EMPTY = 0;

    // The vehicle has a relatively large percentage of seats available.
    // What percentage of free seats out of the total seats available is to be
    // considered large enough to fall into this category is determined at the
    // discretion of the producer.
    MANY_SEATS_AVAILABLE = 1;

    // The vehicle has a relatively small percentage of seats available.
    // What percentage of free seats out of the total seats available is to be
    // considered small enough to fall into this category is determined at the
    // discretion of the feed producer.
    FEW_SEATS_AVAILABLE = 2;

    // The vehicle can currently accommodate only standing passengers.
    STANDING_ROOM_ONLY = 3;

    // The vehicle can currently accommodate only standing passengers
    // and has limited space for them.
    CRUSHED_STANDING_ROOM_ONLY = 4;

    // The vehicle is considered full by most measures, but may still be
    // allowing passengers to board.
    FULL = 5;

    // The vehicle is not accepting additional passengers.
    NOT_ACCEPTING_PASSENGERS = 6;
  }
  optional OccupancyStatus occupancy_status = 9;

  // The extensions namespace allows 3rd-party developers to extend the
  // GTFS Realtime Specification in order to add and evaluate new features and
  // modifications to the spec.
  extensions 1000 to 1999;
}

// An alert, indicating some sort of incident in the public transit network.
message Alert {
  // Time when the alert should be shown to the user. If missing, the
  // alert will be shown as long as it appears in the feed.
  // If multiple ranges are given, the alert will be shown during all of them.
  repeated TimeRange active_period = 1;

  // Entities whose users we should notify of this alert.
  repeated EntitySelector informed_entity = 5;

  // Cause of this alert.
  enum Cause {
    UNKNOWN_CAUSE = 1;
    OTHER_CAUSE = 2;  // Not machine-representable.
    TECHNICAL_PROBLEM = 3;
    STRIKE = 4;         // Public transit agency employees stopped working.
    DEMONSTRATION = 5;  // People are blocking the streets.
    ACCIDENT = 6;
    HOLIDAY = 7;
    WEATHER = 8;
    MAINTENANCE = 9;
    CONSTRUCTION = 10;
    POLICE_ACTIVITY = 11;
    MEDICAL_EMERGENCY = 12;
  }
  optional Cause cause = 6 [default = UNKNOWN_CAUSE];

  // What is the effect of this problem on the affected entity.
  enum Effect {
    NO_SERVICE = 1;
    REDUCED_SERVICE = 2;

    // We don't care about INsignificant delays: they are hard to detect, have
    // little impact on the user, and would clutter the results as they are too
    // frequent.
    SIGNIFICANT_DELAYS = 3;

    DETOUR = 4;
    ADDITIONAL_SERVICE = 5;
    MODIFIED_SERVICE = 6;
    OTHER_EFFECT = 7;
    UNKNOWN_EFFECT = 8;
    STOP_MOVED = 9;
  }
  optional Effect effect = 7 [default = UNKNOWN_EFFECT];

  // The URL which provides additional information about the alert.
  optional TranslatedString url = 8;

  // Alert header. Contains a short summary of the alert text as plain-text.
  optional TranslatedString header_text = 10;

  // Full description for the alert as plain-text. The information in the
  // description should add to the information of the header.
  optional TranslatedString description_text = 11;

  // The extensions namespace allows 3rd-party developers to extend the
  // GTFS Realtime Specification in order to add and evaluate new features
  // and modifications to the spec.
  extensions 1000 to 1999;
}

//
// Low level data structures used above.
//

// A time interval. The interval is considered active at time 't' if 't' is
// greater than or equal to the start time and less than the end time.
message TimeRange {
  // Start time, in POSIX time (i.e., number of seconds since January 1st 1970
  // 00:00:00 UTC).
  // If missing, the interval starts at minus infinity.
  optional uint64 start = 1;

  // End time, in POSIX time (i.e., number of seconds since January 1st 1970
  // 00:00:00 UTC).
  // If missing, the interval ends at plus infinity.
  optional uint64 end = 2;

  // The extensions namespace allows 3rd-party developers to extend the
  // GTFS Realtime Specification in order to add and evaluate new features and
  // modifications to the spec.
  extensions 1000 to 1999;
}

// A position.
message Position {
  // Degrees North, in the WGS-84 coordinate system.
  required float latitude = 1;

  // Degrees East, in the WGS-84 coordinate system.
  required float longitude = 2;

  // Bearing, in degrees, clockwise from North, i.e., 0 is North and 90 is East.
  // This can be the compass bearing, or the direction towards the next stop
  // or intermediate location.
  // This should not be direction deduced from the sequence of previous
  // positions, which can be computed from previous data.
  optional float bearing = 3;

  // Odometer value, in meters.
  optional double odometer = 4;
  // Momentary speed measured by the vehicle, in meters per second.
  optional float speed = 5;

  // The extensions namespace allows 3rd-party developers to extend the
  // GTFS Realtime Specification in order to add and evaluate new features and
  // modifications to the spec.
  extensions 1000 to 1999;
}

// A descriptor that identifies an instance of a GTFS trip, or all instances of
// a trip along a route.
// - To specify a single trip instance, the trip_id (and if necessary,
//   start_time) is set. If route_id is also set, then it should be same as one
//   that the given trip corresponds to.
// - To specify all the trips along a given route, only the route_id should be
//   set. Note that if the trip_id is not known, then stop sequence ids in
//   TripUpdate are not sufficient, and stop_ids must be provided as well. In
//   addition, absolute arrival/departure times must be provided.
message TripDescriptor {
  // The trip_id from the GTFS feed that this selector refers to.
  // For non frequency-based trips, this field is enough to uniquely identify
  // the trip. For frequency-based trip, start_time and start_date might also be
  // necessary.
  optional string trip_id = 1;

  // The route_id from the GTFS that this selector refers to.
  optional string route_id = 5;

  // The direction_id from the GTFS feed trips.txt file, indicating the
  // direction of travel for trips this selector refers to. This field is
  // still experimental, and subject to change. It may be formally adopted in
  // the future.
  optional uint32 direction_id = 6;

  // The initially scheduled start time of this trip instance.
  // When the trip_id corresponds to a non-frequency-based trip, this field
  // should either be omitted or be equal to the value in the GTFS feed. When
  // the trip_id corresponds to a frequency-based trip, the start_time must be
  // specified for trip updates and vehicle positions. If the trip corresponds
  // to exact_times=1 GTFS record, then start_time must be some multiple
  // (including zero) of headway_secs later than frequencies.txt start_time for
  // the corresponding time period. If the trip corresponds to exact_times=0,
  // then its start_time may be arbitrary, and is initially expected to be the
  // first departure of the trip. Once established, the start_time of this
  // frequency-based trip should be considered immutable, even if the first
  // departure time changes -- that time change may instead be reflected in a
  // StopTimeUpdate.
  // Format and semantics of the field is same as that of
  // GTFS/frequencies.txt/start_time, e.g., 11:15:35 or 25:15:35.
  optional string start_time = 2;
  // The scheduled start date of this trip instance.
  // Must be provided to disambiguate trips that are so late as to collide with
  // a scheduled trip on a next day. For example, for a train that departs 8:00
  // and 20:00 every day, and is 12 hours late, there would be two distinct
  // trips on the same time.
  // This field can be provided but is not mandatory for schedules in which such
  // collisions are impossible - for example, a service running on hourly
  // schedule where a vehicle that is one hour late is not considered to be
  // related to schedule anymore.
  // In YYYYMMDD format.
  optional string start_date = 3;

  // The relation between this trip and the static schedule. If a trip is done
  // in accordance with temporary schedule, not reflected in GTFS, then it
  // shouldn't be marked as SCHEDULED, but likely as ADDED.
  enum ScheduleRelationship {
    // Trip that is running in accordance with its GTFS schedule, or is close
    // enough to the scheduled trip to be associated with it.
    SCHEDULED = 0;

    // An extra trip that was added in addition to a running schedule, for
    // example, to replace a broken vehicle or to respond to sudden passenger
    // load.
    ADDED = 1;

    // A trip that is running with no schedule associated to it, for example, if
    // there is no schedule at all.
    UNSCHEDULED = 2;

    // A trip that existed in the schedule but was removed.
    CANCELED = 3;
  }
  optional ScheduleRelationship schedule_relationship = 4;

  // The extensions namespace allows 3rd-party developers to extend the
  // GTFS Realtime Specification in order to add and evaluate new features and
  // modifications to the spec.
  extensions 1000 to 1999;
}

// Identification information for the vehicle performing the trip.
message VehicleDescriptor {
  // Internal system identification of the vehicle. Should be unique per
  // vehicle, and can be used for tracking the vehicle as it proceeds through
  // the system.
  optional string id = 1;

  // User visible label, i.e., something that must be shown to the passenger to
  // help identify the correct vehicle.
  optional string label = 2;

  // The license plate of the vehicle.
  optional string license_plate = 3;

  // The extensions namespace allows 3rd-party developers to extend the
  // GTFS Realtime Specification in order to add and evaluate new features and
  // modifications to the spec.
  extensions 1000 to 1999;
}

// A selector for an entity in a GTFS feed.
message EntitySelector {
  // The values of the fields should correspond to the appropriate fields in the
  // GTFS feed.
  // At least one specifier must be given. If several are given, then the
  // matching has to apply to all the given specifiers.
  optional string agency_id = 1;
  optional string route_id = 2;
  // corresponds to route_type in GTFS.
  optional int32 route_type = 3;
  optional TripDescriptor trip = 4;
  optional string stop_id = 5;

  // The extensions namespace allows 3rd-party developers to extend the
  // GTFS Realtime Specification in order to add and evaluate new features and
  // modifications to the spec.
  extensions 1000 to 1999;
}

// An internationalized message containing per-language versions of a snippet of
// text or a URL.
// One of the strings from a message will be picked up. The resolution proceeds
// as follows:
// 1. If the UI language matches the language code of a translation,
//    the first matching translation is picked.
// 2. If a default UI language (e.g., English) matches the language code of a
//    translation, the first matching translation is picked.
// 3. If some translation has an unspecified language code, that translation is
//    picked.
message TranslatedString {
  message Translation {
    // A UTF-8 string containing the message.
    required string text = 1;
    // BCP-47 language code. Can be omitted if the language is unknown or if
    // no i18n is done at all for the feed. At most one translation is
    // allowed to have an unspecified language tag.
    optional string language = 2;

    // The extensions namespace allows 3rd-party developers to extend the
    // GTFS Realtime Specification in order to add and evaluate new features and
    // modifications to the spec.
    extensions 1000 to 1999;
  }
  // At least one translation must be provided.
  repeated Translation translation = 1;

  // The extensions namespace allows 3rd-party developers to extend the
  // GTFS Realtime Specification in order to add and evaluate new features and
  // modifications to the spec.
  extensions 1000 to 1999;
}