Question

将cAshapelayer半径转换为mkcircle radius转换。

由于shapelayer基于实际视图的顶点，而mkcircle半径基于地图缩放系数，转换的最佳方法是什么？

Answer 1

下面列出了将MKCircle的半径转换为视图和背面的方法之一： -

1＆GT;将MKCircle的中心点（lat，long）转换为ViewController视图的中心点。它将成为CAShapeLayer的中心。

[mapView convertCoordinate:yourCoordinate toPointToView:self.view];

2＆gt; MKCircle将半径作为地图上的距离，以iOS为单位。必须将此距离转换为UIViewController视图上的距离。可以遵循以下步骤来计算相同的步骤。

a）使用以下方法获取距离MKCircle半径r米处的（Lat，Long）： -

-(CLLocationCoordinate2D)calculateCoordinateForDistanceInKm:(double)distanceKM bearing:(double)bearing initialCoordinate:(CLLocationCoordinate2D)coordinate
{
    if(!CLLocationCoordinate2DIsValid(coordinate) || !isValidDouble(distanceKM) || !isValidDouble(bearing))
        assert("The Inputs are not Valid");

    double angularDistance  = tan(distanceKM / 6371.0f);
    double bearingRad       = degreeToRad(bearing);
    double currentLat       = degreeToRad(coordinate.latitude);
    double currentLong      = degreeToRad(coordinate.longitude);

    double newLatitude      = asin((sin(currentLat) * cos(angularDistance))
                                   + (cos(currentLat) * sin(angularDistance) * cos(bearingRad)));
    double newLongitude     = currentLong + atan2(sin(bearingRad)
                                                  * sin(angularDistance) * cos(currentLat), cos(angularDistance) - (sin(currentLat) * sin(newLatitude)));
    // newLongitude should be in the range -180 to +180
    newLongitude           = fmod((newLongitude + 3*M_PI), (2*M_PI)) - M_PI;

    return CLLocationCoordinate2DMake(RadToDegree(newLatitude), RadToDegree(newLongitude));
}

bool isValidDouble(double number)
{
    if(isnan(number) || isinf(number))
        return NO;
    return YES;
}

double degreeToRad(double degree)
{
    double radians  = (degree *  M_PI)/ 180.0f;
    return radians;
}

double RadToDegree(double rad)
{
    double degree   = (rad *  180.0f)/ M_PI;
    return degree;
}

b）将新坐标翻译为步骤1中提到的UIViewController视图。

c）找出这两点之间的距离。

CGPoint pointOne = [mapView convertCoordinate:yourCoordinate toPointToView:self.view];
CLLocationCoordinate2D newCoordinate = [self calculateCoordinateForDistanceInKm:1.0f bearing:youtCurrentLocationObject.course initialCoordinate:youtCurrentLocationObject.coordinate];
CGPoint pointTwo = [mapView convertCoordinate:newCoordinate toPointToView:self.view];
NSNumber *radius = [NSNumber numberWithDouble:hypotf(pointOne.x - pointTwo.x, pointOne.y - pointTwo.y)];

3）根据半径和第一个点（圆心）绘制CAShapeLayer。

4）将CAShapeLayer点bak转换为CLLocationCoordinate2D以绘制MKCircle（在满足您的某些要求之后）。 CAShapeLayer的中心点和半径已知，因此中心将是(x,y)，并且距中心等距的轨迹上的点将为(x + radius, y)。

使用以下命令将视图的点转换回MKMapView的坐标。

[mapView convertPoint:someCGPoint toCoordinateFromView:mapView]

注意： - 用于计算距离另一个坐标的距离为D的坐标的公式。

Formula:    φ2 = asin( sin φ1 ⋅ cos δ + cos φ1 ⋅ sin δ ⋅ cos θ )
    λ2 = λ1 + atan2( sin θ ⋅ sin δ ⋅ cos φ1, cos δ − sin φ1 ⋅ sin φ2 )
where   φ is latitude, λ is longitude, θ is the bearing (clockwise from north), δ is the angular distance d/R; d being the distance travelled, R the earth’s radius.

希望它能回答你的问题。

考虑到缩放系数，将CAShapeLayer raidus转换为MKcircle半径

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