Comparing two locations using their Longitude and Latitude

问题

Hi i need to cal an event at onchangelocation(), by comparing current latitude and longitude with some saved latitude and longitude but i m getting an error. eclipse is not recognizing key word distance, and for correction error it is giving hint to crate method "distance" having 4 parameter ... how to fix it??? or some other way to do same work???

thanks and regards. code is attached below

@Override
public void onLocationChanged(Location location) {
 double currentLat=location.getLatitude();
 double currentLon=location.getLongitude();

    if (distance(lat,lon,currentLat,currentLon)<2.0){
 //do what you want to do...
  }
}

回答1:

You actually need to implement a function called distance that will calculate the distance between two locations. Calculating the distance between two locations is one possible way of comparing the longitude and latitude values.

An example of comparing them:

@Override
public void onLocationChanged(Location location) {

 double lat2 = location.getLatitude();
 double lng2 = location.getLongitude();

    // lat1 and lng1 are the values of a previously stored location
    if (distance(lat1, lng1, lat2, lng2) < 0.1) { // if distance < 0.1 miles we take locations as equal
       //do what you want to do...
    }
}

/** calculates the distance between two locations in MILES */
private double distance(double lat1, double lng1, double lat2, double lng2) {

    double earthRadius = 3958.75; // in miles, change to 6371 for kilometer output

    double dLat = Math.toRadians(lat2-lat1);
    double dLng = Math.toRadians(lng2-lng1);

    double sindLat = Math.sin(dLat / 2);
    double sindLng = Math.sin(dLng / 2);

    double a = Math.pow(sindLat, 2) + Math.pow(sindLng, 2)
        * Math.cos(Math.toRadians(lat1)) * Math.cos(Math.toRadians(lat2));

    double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));

    double dist = earthRadius * c;

    return dist; // output distance, in MILES
}

回答2:

You can use the Location class's static distanceBetween() method like so:

    float[] distance = new float[1];
    Location.distanceBetween(lat, lon, currentLat, currentLon, distance);
    // distance[0] is now the distance between these lat/lons in meters
    if (distance[0] < 2.0) {
        // your code...
    }

If you have two Location objects, another option is distanceTo()

回答3:

All the 4 input parameters are in float. Distance is a relative one not real distance. You need to convert this distance to a real distance by searching some formula online :( I used this in my app to get nearest metro station from my current location. Hope this snippet helps someone :)

float distance(float lat,float lon,float clat,float clon)
{
    float distance;
    float temp1;
    float temp2;
    temp1=(float)((lat-clat)*(lat-clat));
    temp2=(float)((lon-clon)*(lon-clon));
    distance=temp1+temp2;
    return distance;
}

来源：https://stackoverflow.com/questions/18170131/comparing-two-locations-using-their-longitude-and-latitude