How to get radius from visible area of MKmapview?

问题

I am able to get visible rectangle of map view and also centre point of map view and span deltas are also get from mkmaap view methods: To get visible are :mapView.visibleMapRect is used . To get centre point: map view.centerCoordinate is used and to get span: mapView.region.span is used.

Now I have all the information, how can i calculate radius of visible are using calculation? Can anyone explain me in detail?

I have seen this question but the answer is giving me span not radius of visible area.

回答1:

To get the radius follow this:

- (CLLocationDistance)getRadius
{
    CLLocationCoordinate2D centerCoor = [self getCenterCoordinate];
    // init center location from center coordinate
    CLLocation *centerLocation = [[CLLocation alloc] initWithLatitude:centerCoor.latitude longitude:centerCoor.longitude];

    CLLocationCoordinate2D topCenterCoor = [self getTopCenterCoordinate];
    CLLocation *topCenterLocation = [[CLLocation alloc] initWithLatitude:topCenterCoor.latitude longitude:topCenterCoor.longitude];

    CLLocationDistance radius = [centerLocation distanceFromLocation:topCenterLocation];

    return radius;
}

It will return the radius in metres.

To get center coordinate

- (CLLocationCoordinate2D)getCenterCoordinate
{
    return [self.mapView centerCoordinate];
}

For getting radius, depends on where you want to get the 2nd point. Lets take the Top Center

- (CLLocationCoordinate2D)getTopCenterCoordinate
{
    // to get coordinate from CGPoint of your map
    return [self.mapView convertPoint:CGPointMake(self.mapView.frame.size.width / 2.0f, 0) toCoordinateFromView:self.mapView];
}

回答2:

With Swift 3.0 you can use extension to simplify your life:

extension MKMapView {

    func topCenterCoordinate() -> CLLocationCoordinate2D {
        return self.convert(CGPoint(x: self.frame.size.width / 2.0, y: 0), toCoordinateFrom: self)
    }

    func currentRadius() -> Double {
        let centerLocation = CLLocation(coordinate: self.centerCoordinate)
        let topCenterCoordinate = self.topCenterCoordinate()
        let topCenterLocation = CLLocation(coordinate: topCenterCoordinate)
        return centerLocation.distance(from: topCenterLocation)
    }

}

With Swift 4.0 :

extension MKMapView {

    func topCenterCoordinate() -> CLLocationCoordinate2D {
        return self.convert(CGPoint(x: self.frame.size.width / 2.0, y: 0), toCoordinateFrom: self)
    }

    func currentRadius() -> Double {
        let centerLocation = CLLocation(latitude: self.centerCoordinate.latitude, longitude: self.centerCoordinate.longitude)
        let topCenterCoordinate = self.topCenterCoordinate()
        let topCenterLocation = CLLocation(latitude: topCenterCoordinate.latitude, longitude: topCenterCoordinate.longitude)
        return centerLocation.distance(from: topCenterLocation)
    }

}

来源：https://stackoverflow.com/questions/29093843/how-to-get-radius-from-visible-area-of-mkmapview

标签

ios

swift

mkmapview