与长距离线段的距离在长距离错误 [英] Distance from long lat line segment wrong over long distances

问题描述

我的功能似乎有效，但随着我增加了距离，它是清除它不工作。我认为这是由于地球的曲率造成的。在我的计算中，罗马显示为距离线5公里。

• 伦敦，英国 - 0公里


• 罗马，意大利 - 5公里


• li>
  

但在Google Earth上，它实际上更像是61km

当我开始走得更远时，计算变得更糟！

• 罗马，意大利 - 0公里


• Mohenjo-daro，巴基斯坦 - 0公里
  
• 伊斯坦布尔，土耳其 - 250km

我相信这个问题出现在代码的某处：

  function distToSegment（lat1，lon1，lat2，lon2，lat3，lon3）{
 var y = Math.sin（lon3  -  lon1）* Math.cos（lat3）; 
 var x = Math.cos（lat1）* Math.sin（lat3） -  Math.sin（lat1）* Math.cos（lat3）* Math.cos（lat3  -  lat1）; 
 var bearing1 = radiansToDegrees（Math.atan2（y，x））; 
 bearing1 = 360  - （bearing1 + 360％360）; 
 var y2 = Math.sin（lon2  -  lon1）* Math.cos（lat2）; 
 var x2 = Math.cos（lat1）* Math.sin（lat2） -  Math.sin（lat1）* Math.cos（lat2）* Math.cos（lat2  -  lat1）; 
 var bearing2 = radiansToDegrees（Math.atan2（y2，x2））; 
 bearing2 = 360  - （bearing2 + 360％360）; 
 var lat1Rads = degreesToRadians（lat1）; 
 var lat3Rads = degreesToRadians（lat3）; 
 var dLon = degreesToRadians（lon3  -  lon1）; 
 var distanceAC = Math.acos（Math.sin（lat1Rads）* Math.sin（lat3Rads）+ Math.cos（lat1Rads）* Math.cos（lat3Rads）* Math.cos（dLon））* 6371; （数学.asin（Math.sin（distanceAC / 6371）* Math.sin（degreesToRadians（bearing1） -  degreesToRadians（bearing2）））* 6371）; 
 var min_distance = Math.abs 
返回min_distance; 
 
  

这是一个可以用来测试的小工具：

http://jsfiddle.net/kmturley/cfg2D/3 /

任何有助于找出这个问题的方法都将不胜感激！

解决方案

  bearing1 = 360  - （bearing1 + 360％360）
  

看上去很腥。你的意思是：
$ b $ pre $ bearing1 = 360 - （bearing1 + 360）％360


？

同样对于 bearing2 。

％是一个乘法运算符，优先级高于 + 。

I am calculating how far away a point is from a line segment on the earth.

My function seemed to work, but as i've increased the distances it's clear it's not working. I presume this is due to the curvature of the earth.

In my calculations Rome is shown as 5km from the line:

• London, UK - 0km
• Rome, Italy - 5km
• Cyrene, Libya - 0km

But on Google Earth it's actually more like 61km

When I start going longer distances the calculations get even worse!

• Rome, Italy - 0km
• Mohenjo-daro, Pakistan - 0km
• Istanbul, Turkey - 250km

I believe the problem is somewhere in the code here:

function distToSegment(lat1, lon1, lat2, lon2, lat3, lon3) {
    var y = Math.sin(lon3 - lon1) * Math.cos(lat3);
    var x = Math.cos(lat1) * Math.sin(lat3) - Math.sin(lat1) * Math.cos(lat3) * Math.cos(lat3 - lat1);
    var bearing1 = radiansToDegrees(Math.atan2(y, x));
    bearing1 = 360 - (bearing1 + 360 % 360);
    var y2 = Math.sin(lon2 - lon1) * Math.cos(lat2);
    var x2 = Math.cos(lat1) * Math.sin(lat2) - Math.sin(lat1) * Math.cos(lat2) * Math.cos(lat2 - lat1);
    var bearing2 = radiansToDegrees(Math.atan2(y2, x2));
    bearing2 = 360 - (bearing2 + 360 % 360);
    var lat1Rads = degreesToRadians(lat1);
    var lat3Rads = degreesToRadians(lat3);
    var dLon = degreesToRadians(lon3 - lon1);
    var distanceAC = Math.acos(Math.sin(lat1Rads) * Math.sin(lat3Rads) + Math.cos(lat1Rads) * Math.cos(lat3Rads) * Math.cos(dLon)) * 6371;  
    var min_distance = Math.abs(Math.asin(Math.sin(distanceAC / 6371) * Math.sin(degreesToRadians(bearing1) - degreesToRadians(bearing2))) * 6371);
    return min_distance;
}

Here is a working fiddle you can use to test:

http://jsfiddle.net/kmturley/cfg2D/3/

Any help to figure this one out would be appreciated!

解决方案

This

bearing1 = 360 - (bearing1 + 360 % 360)

looks fishy to me. Do you mean

bearing1 = 360 - (bearing1 + 360) % 360

?

Likewise for bearing2.

% is a multiplicative operator and has higher precedence than +.

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