Java Math.toRadians(angle)与硬计算 [英] Java Math.toRadians(angle) vs hard-calculated

问题描述

这个问题与另一个stackoverflow讨论有关

This question is related to another stackoverflow discussion distance between long&lat points

以下是投票结果最高的答案中的代码:

Here is the code from the top voted answer:

/*
 * Calculate distance between two points in latitude and longitude taking
 * into account height difference. If you are not interested in height
 * difference pass 0.0. Uses Haversine method as its base.
 * 
 * lat1, lon1 Start point lat2, lon2 End point el1 Start altitude in meters
 * el2 End altitude in meters
 */
private double distance(double lat1, double lat2, double lon1, double lon2,
        double el1, double el2) {

    final int R = 6371; // Radius of the earth

    Double latDistance = deg2rad(lat2 - lat1);
    Double lonDistance = deg2rad(lon2 - lon1);
    Double a = Math.sin(latDistance / 2) * Math.sin(latDistance / 2)
            + Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2))
            * Math.sin(lonDistance / 2) * Math.sin(lonDistance / 2);
    Double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
    double distance = R * c * 1000; // convert to meters

    double height = el1 - el2;
    distance = Math.pow(distance, 2) + Math.pow(height, 2);
    return Math.sqrt(distance);
}

private double deg2rad(double deg) {
    return (deg * Math.PI / 180.0);
}

投票得最高的答案有以下评论:

The top voted answer has the following comment:

为什么不使用Math.toRadians()而不是deg2rad()?它确实是自包含的."

"Why not Math.toRadians() instead of deg2rad()? It would be really self-containing."

我在

I looked up the Math.toRadians() method in the documentation and noticed this:

将以度为单位的角度转换为以弧度为单位的近似等效角度.从度到弧度的转换通常是不精确的."

"Converts an angle measured in degrees to an approximately equivalent angle measured in radians. The conversion from degrees to radians is generally inexact."

1. 投票最多的答案的deg2rad方法是否比Math.toRadians()方法更精确?
2. 使用deg2rad方法执行两项算术运算，并执行一次Math.Pi查找，尚不清楚Math.toRadians()如何执行约定.假设此距离计算可能会频繁执行并且需要对用户输入的快速响应，那么哪种转换方法将更有效地扩展规模?

如果问题1的答案是两种方法的不精确性/准确性大致相同，那么我认为我将使用Math.toRadians.使用Math.ToRadians可使代码更具可读性，并且我认为它也将更有效地扩展.

If the answer to question 1 is that the two methods have roughly the same inexactness/accuracy, I think that I would use Math.toRadians. Using Math.ToRadians makes the code more readable, and I assume that it would scale more efficiently as well.

推荐答案

Math.toRadians是这样实现的:

public static double toRadians(double angdeg) {
    return angdeg / 180.0 * PI;
}

1)如果存在差异，则可以忽略不计. Math.toRadians首先进行除法，而答案首先进行乘法.

1) If there is a difference, it's negligible. Math.toRadians does the division first, while that answer does the multiplication first.

2)唯一可以确定的方法是对其进行测试，但是我希望它们都不会更快，因为它们都做同样的事情.

2) The only way to find out for sure is to test it, but I would expect that neither is faster since they both do the same thing.

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