使用Core Data查找距离lat / long最近的 [英] Find nearest by lat/long with Core Data

问题描述

我有一个带有Core Data数据库的iPhone应用程序，其中包含位置列表，每个位置都有纬度/经度坐标。我如何搜索说到最近的10到我当前的位置？

I have an iPhone app with a Core Data database containing a list of locations, each with lat/long coordinates. How can I search for say the nearest 10 to my current location?

我是Core Data的新用户，所以我的问题是如何做查找，我知道如何获取我当前的位置等等。我相信我需要设置一个查询词NSPredicate，但不知道应该如何写。

I'm new to Core Data so my question is really how to do the lookup, I know how to get my current location etc. I believe I need to setup an NSPredicate with a query term but not sure exactly how that should be written.

谢谢，
J

Thanks, J

推荐答案

您可以尝试此操作（ reference ）

double M_PI = 3.141592653589793;
#define d2r (M_PI / 180.0)

    double haversine_km(double lat1, double long1, double lat2, double long2) {
        double dlong = (long2 - long1) * d2r;
        double dlat = (lat2 - lat1) * d2r;
        double a = pow(sin(dlat/2.0), 2) + cos(lat1*d2r) * cos(lat2*d2r) * pow(sin(dlong/2.0), 2);
        double c = 2 * atan2(sqrt(a), sqrt(1-a));
        double distance = 6367 * c;

        return distance;
    }

    - (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {
        /*Calculate distance of all locations in DB and current location. If diff. between any stop is less than x meters, perform desired operation*/
        NSArray *listLocationsFromDB = [self getLocations]; //Get all locations from DB
        for (Location *location in listLocationsFromDB) {
            double distance = haversine_km(newLocation.coordinate.latitude, newLocation.coordinate.longitude, [location.latitude doubleValue], [location.longitude doubleValue]);
            distance *= 1000;
            if (distance <= 200) {  //200 meters
                //Your code here
            }
        }   
    }

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