iPhone 指南针 GPS 方向 [英] iPhone Compass GPS Direction

问题描述

我正在尝试开发一个使用 iPhone 的 GPS 和指南针的应用程序，以便将某种指针指向特定位置(例如指南针总是指向北方).该位置是固定的，无论用户位于何处，我总是需要指针指向该特定位置.我有这个位置的纬度/经度坐标，但不知道如何使用指南针和 GPS 指向那个位置......就像 http://www.youtube.com/watch?v=iC0Xn8hY80w 这个链接 1:20'

I'm trying to develop an application that use the GPS and Compass of the iPhone in order to point some sort of pointer to a specific location (like the compass always point to the North). The location is fixed and I always need the pointer to point to that specific location no matter where the user is located. I have the Lat/Long coordinates of this location but not sure how can I point to that location using the Compass and the GPS... just like http://www.youtube.com/watch?v=iC0Xn8hY80w this link 1:20'

我写了一些代码，但是它不能向右旋转.

I write some code, however, it can't rotate right direction.

-(float) angleToRadians:(double) a {
    return ((a/180)*M_PI);
}

-(void)updateArrow {    
    double alon=[longi doubleValue];//source
    double alat=[lati doubleValue];//source
    double blon=[pointlongi doubleValue];//destination
    double blat=[pointlati doubleValue];//destination

    float fLat = [self angleToRadians:alat];
    float fLng = [self angleToRadians:alon];
    float tLat = [self angleToRadians:blat];
    float tLng = [self angleToRadians:blon];

    float temp = atan2(sin(tLng-fLng)*cos(tLat), 
        cos(fLat)*sin(tLat)-sin(fLat)*cos(tLat)*cos(tLng-fLng)); 
    double temp2= previousHeading;

    double temp1=temp-[self angleToRadians:temp2];

    /*I using this,but it can't rotate by :point even i change the coordinate
      in CGPointMake */
    Compass2.layer.anchorPoint=CGPointMake(0, 0.5);

    [Compass2 setTransform:CGAffineTransformMakeRotation(temp1)];
    /* Compass2 is a UIImageView like below picture I want to rotate it around 
     : point in image

        ^
        |
        | 
        |
        :
        |
    */

推荐答案

有一个标准的航向"或方位"方程可以使用——如果你在 lat1,lon1，你感兴趣的点是在 lat2,lon2，则方程为:

There is a standard "heading" or "bearing" equation that you can use - if you are at lat1,lon1, and the point you are interested in is at lat2,lon2, then the equation is:

heading = atan2( sin(lon2-lon1)*cos(lat2), cos(lat1)*sin(lat2) - sin(lat1)*cos(lat2)*cos(lon2-lon1))

这为您提供了以弧度为单位的方位，您可以通过乘以 180/π 将其转换为度数.然后该值介于 -180 和 180 度之间，因此要获得标准指南针方位，请在任何否定答案上加上 360.

This gives you a bearing in radians, which you can convert to degrees by multiplying by 180/π. The value is then between -180 and 180 degrees, so to get a standard compass bearing add 360 to any negative answers.

atan2 是一个与 arctan 相关的标准函数，与您所在的位置相比，它对您的目标点可能位于的四个可能的象限执行正确的操作.

atan2 is a standard function related to arctan, that does the right thing for the four possible quadrants that your destination point could be in compared to where you are.

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