iPhone Compass GPS方向 [英] iPhone Compass GPS Direction

问题描述

我试图开发一个应用程序，使用iPhone的GPS和指南针来指向某个特定位置的某种指针（例如指南针始终指向北方）。该位置是固定的，我总是需要指针指向该特定位置，而不管用户位于何处。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 此链接1:20'

I写一些代码，但是，它不能正确旋转。

   - （float）angleToRadians：（double）a {
回报（（a / 180）* M_PI）; 
 
 $ b  - （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]; 
 
 / *我使用这个，但它不能旋转：点即使我改变坐标
 CGPointMake * / 
 Compass2.layer.anchorPoint = CGPointMake（0， 0.5）; 
 
 [Compass2 setTransform：CGAffineTransformMakeRotation（temp1）]; 
 / * Compass2是一个UIImageView，如下图所示我想将它旋转
：point in image 
 
 ^ 
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 | 
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：
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 * / 
  

解决方案

您可以使用标题或方位方程 - 如果您位于lat1，lon1，并且您感兴趣的点位于lat2，lon2，则方程为：

（lat2），cos（lat1）* sin（lat2）-sin（lat1）* cos（lat2）* cos（lat2）* sin（lat1） lon2-lon1））

这给你一个弧度方位，你可以通过乘以180 /π。这个值是在-180和180度之间，所以要得到一个标准的指南针方位，可以给360加上任何的负面答案。

atan2是一个与arctan相关的标准函数，为您的目的地可能会出现的四个象限做出正确的选择。

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'

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

        ^
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        :
        |
    */

解决方案

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))

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 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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