为什么 GTFS 这么难？

Why is GTFS so difficult?

我正在尝试创建一个基于 Arduino 的显示器，显示纽约市地铁北站接下来几列火车的时间。 Metro North 由 MTA 运行（MTA 是纽约市地铁和公共汽车机构）和 I had no trouble creating a similar display for MTA busses. 但是，火车数据非常困难。它不能通过 URL 中的 GET 命令过滤。我必须自己解析数据才能获得停止级别的数据。 （由火车组织。）

我有网页可以运行简单PHP、java等。我想我需要创建一个页面来解析"json"/"XML" 文件从 MTA 给我。然后 Arduino 可以使用简化的数据。我可以使用 URL 和我的 api 密钥获取实时数据。这是它的样子：

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就像从消防水带里喝水一样。

它采用一种名为 GTFS 的格式，应该是 "universal"，但我发现很难找到适用于它的任何格式。 For example, simplexml_load_file() in PHP won't work.

Arduino 不适合解析文本。我不能强迫 Arduino 完成所有工作。

我应该学习什么方法？我对我的服务器没有太多控制权。我无法轻易更改服务器上 PHP 运行 的方式。到目前为止我发现的方法似乎需要扩展和其他我做不到的事情。

是的，"drinking from a firehose" 是使用 GTFS 数据的一个很好的比喻。 GTFS 的一方面是将运输机构系统的负载降到最低，并让应用程序开发人员的系统（您）完成尽可能多的工作。这两部分（包含当前路线信息的 "static" GTFS 文件和 GTFS 实时文件）都可以是静态数据文件，由 "dumb" 网络服务器提供（不需要网络应用程序代码），这使得提供数据非常方便可扩展。

一些交通机构（如 MTA，就其公交路线而言）很好，可以为您完成一些工作，提供 XML 或 JSON API为您提供特定路线的当前实时状态。但是，如果您学会了如何在您这边处理 GTFS 数据，您就不需要依赖他们 API，您的系统将变得 "universal"，能够处理任何提供 GTFS 实时信息的机构。

我猜你已经看过文档了，但为了以防万一，这里有参考资料：https://developers.google.com/transit/

通常，您会结合使用 GTFS 文件（包含日历、路线、行程、停靠点和 stop_times）和 GTFS 实时文件（特别是 tripUpdate 文件）来确定车辆的当前状态与其当前行程的停靠点有关。他们可能只是给你车辆在当前行程中的延迟时间，然后你需要查找目标站点每次行程的停止时间，并根据相应的延迟进行调整。

但是，MTA 又变好了，他们只在实时提要中为您提供足够的信息，以显示车辆（例如 1586 号火车）何时将到达一个站点（例如 144 号站点）一次（例如 unix 时间 1442890020 = 2015 年 9 月 22 日星期二 02:47:00 GMT）和延迟（例如 60 秒）。

因此，如果您的 PHP 流程正在尝试为目标站点创建即将到来的出发时间列表，您将：

  1. 将实时提要解析为对象集合（我假设您可以在 PHP 中执行此操作，正如上面提到的 Twisty 使用 json_decode()）
  2. 遍历 "trip_update" 个对象的数组
  3. 在"stop_time_update"对象下，遍历"departure"个对象的数组
  4. 对于每个 "departure" 的 "stop_id" 与您希望设备显示其信息的站点相匹配，将其 "time" 值（unix 时间）添加到集合中。
  5. 对生成的集合进行排序，并将其从 unix 时间转换为任何 PHP 的本地日期时间对象，并将其格式化为文本
  6. 将接下来的两个出发时间发送到您的设备

对于这个案例，这将是您的快速解决方案。