iPhone 4后台定位服务问题
我正在研究 iPhone 4 SDK 中新的后台位置服务选项。它允许应用程序在后台运行并从设备接收位置更新。
提供了两种方法。一种是电池密集型模式，可以持续获取位置更新。第二种推荐的方法是在发生“重大位置变化”时发送应用程序位置更新。
有谁知道重大位置变化可能是什么？ 30 英尺的步行是否被认为是重要的，或者 10 个街区的步行是否被认为是重要的？我想这还取决于当时使用的定位机制的准确性。
I'm looking into the new background location service options in the iPhone 4 SDK. It allows an app to run in the background and receive location updates from the device.
There are two methods offered. One is a battery intensive mode that continuously gets location updates. The second recommended method sends the app location updates when there has been a "significant location change".
Does anyone know what a significant location change might be? Is a 30 foot walk considered significant, or is a 10 block walk considered significant? I imagine it also depends on the accuracy of the location mechanism being used at the time.
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正如史蒂夫·乔布斯在 OS 4 介绍中提到的，低功耗模式使用蜂窝塔三角测量并且不激活 GPS 单元。由于 iPhone 手机模块无论如何都需要保持与手机网络的连接，因此不会对电池寿命产生影响。
由于使用蜂窝塔三角测量进行定位的精度介于几十米（在人口稠密的城市位置）和几英里之间，因此我认为 30 英尺并不是一个重大的位置变化。不过，我不知道具体细节（正如评论者提到的，苹果开发者论坛是讨论这些问题的正确场所）。
As Steve Jobs mentioned in the OS 4 introduction, the low power mode uses cell tower triangulation and does not activate GPS unit. Since the iPhone phone module needs to keep a connection to the cell network anyway, there should be no impact on battery life.
Since the precision of a location fix with cell tower triangulation is anywhere between a few dozen meters (in dense city locations) and a few miles, I think 30 ft is not a significant location change. I don't know the specifics, though (and as mentioned by the commenters, the Apple dev forums are the right place to talk about those).
我最近对新的后台位置服务进行了一些现场测试，以了解什么构成了重要的位置更新、位置命中的准确度以及我们使用它的一般经验。
结果在一篇相当长的博客文章中有详细介绍：
iPhone 后台 GPS：精确到 500 米，不足以满足人流量
I've recently done some field testing of the new background location service to get an idea of what constitutes a significant location update, what kind of accuracy to expect for the location hits and our general experiences using it.
The results are detailed in a fairly lengthy blog post:
iPhone Background GPS: Accurate to 500 meters, not enough for foot traffic