calculate distance between 2 coordinates iphone - best practice

Question

I'm finishing an App in wish i need to show the user the distance between him and about 500 coordinates.

using the CLLocation method to calculate it, works well, but it takes about 1 minute in iPhone 4 to finish calculations for each location.

What is the best way to do it? Using span? Any other faster way?

Thanks all,

rui

Answer 1

I think Sahgal is right, here is some code, perhaps it will help you.

+(CGFloat)calculateDistanceBetweenSource:(CLLocationCoordinate2D)firstCoords andDestination:(CLLocationCoordinate2D)secondCoords 
{

    // this radius is in KM => if miles are needed it is calculated during setter of Place.distance

    double nRadius = 6371;

    // Get the difference between our two points

    // then convert the difference into radians

    double nDLat = (firstCoords.latitude - secondCoords.latitude)* (M_PI/180);
    double nDLon = (firstCoords.longitude - secondCoords.longitude)* (M_PI/180);

    double nLat1 =  secondCoords.latitude * (M_PI/180);
    double nLat2 =  secondCoords.latitude * (M_PI/180);

    double nA = pow ( sin(nDLat/2), 2 ) + cos(nLat1) * cos(nLat2) * pow ( sin(nDLon/2), 2 );

    double nC = 2 * atan2( sqrt(nA), sqrt( 1 - nA ));

    double nD = nRadius * nC;

    NSLog(@"Distance is %f",nD);

    return nD; // converts to miles or not (if en_) => implicit in method
}

Answer 2

You can try another approach.You can fetch the lat-long of both the points(assuming lat-long finding will not take that much time) and there are formulae to calculate the distance using lat-long.

Answer 3

Here is code for that..

-(NSString *)findDistanceBetweenTwoLatLon
{
    int intEarthRadius = 3963;

    double dblLat1 = DegreesToRadians(firstLatitude);
    double dblLon1 = DegreesToRadians(firstLongitude);

    double dblLat2 = DegreesToRadians(secondLatitude);
    double dblLon2 = DegreesToRadians(secondLongitude);

    float fltLat = dblLat2 - dblLat1;
    float fltLon = dblLon2 - dblLon1;

    double a = sin(fltLat/2) * sin(fltLat/2) + cos(dblLat2) * cos(dblLat2) * sin(fltLon/2) * sin(fltLon/2) ;
    double c = 2 * atan2(sqrt(a), sqrt(1-a));
    double d = intEarthRadius * c;

    double dMeters = d * kOneMileMeters;

    NSString *strDistance = [NSString stringWithFormat:@"%1.2f meters",dMeters];

    return strDistance;
}

Define all this Macro..

and for degrees to radians

#define DegreesToRadians(degrees) (degrees * M_PI / 180)

where M_PI

#define M_PI   3.14159265358979323846264338327950288 
#define kOneMileMeters 1609.344

Answer 4

I have seen the other answers, don't know if they are right, but I think there is a better solution:

(from documentation):

- (CLLocationDistance)distanceFromLocation:(const CLLocation *)location

You can use it like this:

- (CLLocationDistance) DistanceBetweenCoordinate:(CLLocationCoordinate2D)originCoordinate andCoordinate:(CLLocationCoordinate2D)destinationCoordinate {

        CLLocation *originLocation = [[CLLocation alloc] initWithLatitude:originCoordinate.latitude longitude:originCoordinate.longitude];
        CLLocation *destinationLocation = [[CLLocation alloc] initWithLatitude:destinationCoordinate.latitude longitude:destinationCoordinate.longitude];
        CLLocationDistance distance = [originLocation distanceFromLocation:destinationLocation];
        [originLocation release];
        [destinationLocation release];

        return distance;
    }