通过距离位置计算MAX和MIN纬度和经度 - 目标C. [英] Calculating MAX and MIN Latitude and Longitude with distance from Location - Objective C

问题描述

我需要从具有一定距离的位置计算MAX和MIN纬度和经度值。

I need to compute MAX and MIN Latitude and Longitude values from a location with certain distance.

我有数千个位置存储在CoreData中，我想显示只有距用户位置5公里范围内的那些。

I have thousands of locations stored in CoreData, and I want to show only the ones within 5km from users location.

我该如何处理这个问题？

How can I approach this problem?

推荐答案

这是一个可能的解决方案：

Here's a possible solution:

1. 将度数转换为Radians的宏

1. macros to convert Degrees to Radians

#define deg2rad(degrees) ((degrees) / 180.0 M_PI)

宏来保持我的搜索距离

macros to hold my searching distance

#define searchDistance 5.00 //float value in KM

设置最小和最大纬度，经度值

set the minimum and maximum Latitude, Longitude values

float minLat = userLocation.coordinate.latitude - (searchDistance / 69);
float maxLat = userLocation.coordinate.latitude + (searchDistance / 69);
float minLon = userLocation.coordinate.latitude - searchDistance / fabs(cos(deg2rad(userLocation.coordinate.latitude))*69);
float maxLon = userLocation.coordinate.longitude + searchDistance / fabs(cos(deg2rad(userLocation.coordinate.latitude))*69);

按如下方式创建谓词

create predicate as follows

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"latitude <= %f AND latitude >= %f AND longitude <= %f AND longitude >= %f", maxLat, minLat, maxLon, minLon];

这将在<$ c周围创建一个正方形$ c> userLocation 并检查给定位置是否落入其坐标。

This will create a square around userLocation and check if a given location falls into its coordinates.

更新：Swift 2. *实现

Update: Swift 2.* implementation

首先创建一个计算度数到弧度的函数

First create a function to compute degrees to radians

func deg2rad(degrees:Double) -> Double{
    return degrees * M_PI / 180
}

计算并创建最小值和最大纬度和经度值

Compute and create minimum and maximum Latitude and Longitude values

let searchDistance:Double =  5.00 //float value in KM    

let minLat = userLocation.coordinate.latitude - (searchDistance / 69)
let maxLat = userLocation.coordinate.latitude + (searchDistance / 69)

let minLon = userLocation.coordinate.longitude - searchDistance / fabs(cos(deg2rad(userLocation.coordinate.latitude))*69)
let maxLon = userLocation.coordinate.longitude + searchDistance / fabs(cos(deg2rad(userLocation.coordinate.latitude))*69)

上次创建 NSPredicate ，查询位置的 CoreData 。在我的情况下，我正在查询值纬度和经度但是你应该更改它以匹配你的 CoreData object

Last create NSPredicate to query CoreData for locations. In my case I am querying for values latitude and longitude but you should change this to match your CoreData object

let predicate = NSPredicate(format: "latitude <= \(maxLat) AND latitude >= \(minLat) AND longitude <= \(maxLon) AND longitude >= \(minLon)")

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