核心数据和核心位置 [英] Core Data and Core Location

问题描述

我有一个具有纬度和经度属性的Core Data数据库。有没有办法使用Core Location的 getDistanceFrom：方法来找到从GPS获得的 CLLocation 的五个最近位置？我必须使用Core Data加载所有对象，并使用 getDistanceFrom：在每个对象上进行解析，还是有更简单的方法？

I have a Core Data database with latitude and longitude properties. Is there a way to use Core Location's getDistanceFrom: method to find the five nearest locations to a CLLocation obtained from the GPS? Do I have to load all the objects using Core Data and parse through them, using getDistanceFrom: on each one or is there an easier way?

推荐答案

你必须逐个迭代它们;但我知道没有其他方法可以做到。

You will have to iterate through them one by one; as far as I know there is no other way to do it.

但是，当您从核心数据获取项目时，可以通过使用边界框使这更有效 - 这将减少将返回的对象的数量。

However, you can make this more efficient by using a bounding box when you get the items from core data - this will reduce the number of objects that will be returned.

ie像

float latMax = wantedLat + 1;
float latMin = wantedLat - 1;
float lngMax = wantedLng + 1;
float lngMin = wantedLng - 1;
NSPredicate *predicate = [NSPredicate
    predicateWithFormat:@"lat > %f and lat < %f and lng > %f and lng < %f",
    latMin, latMax, lngMin, lngMax];

虽然，根据你有多少数据以及间隔多近，不同于1的数字！

Though, depending on how much data you have and how closely it's spaced, you will want to use a different number than 1!

Sam

PS此外，我没有考虑经度包装！

PS Also, I haven't taken into account the fact that longitude wraps!

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