問(wèn)題描述

我有一個(gè)三個(gè)緯度坐標(biāo)，它們組成兩條線段 A 到 B 到 C.我還發(fā)現(xiàn)了一個(gè)函數(shù)，可以以 -180 到 180 的方式返回線段 A-B 或 B-C 的北向.但是，我無(wú)法確定汽車何時(shí)從 A 到達(dá) B，應(yīng)該右轉(zhuǎn)還是左轉(zhuǎn)繼續(xù)前往 C.

I have a three lat-lon coordinates that make up two line segment A to B to C. I also found a function that can return north-bearing of a line segment A-B or B-C in -180 to 180 manner. However, I'm having trouble to determine when a car reaches from A to B, should it turn right or left to continue to C.

推薦答案

之前的答案是錯(cuò)誤的.現(xiàn)在這是正確的

Previous answer was wrong. now this is the correct

public Direction GetDirection(Point a, Point b, Point c)
{
    double theta1 = GetAngle(a, b); 
    double theta2 = GetAngle(b, c);
    double delta = NormalizeAngle(theta2 - theta1);

    if ( delta == 0 )
        return Direction.Straight;
    else if ( delta == Math.PI )
        return Direction.Backwards;
    else if ( delta < Math.PI )
        return Direction.Left;
    else return Direction.Right;
}

private Double GetAngle(Point p1, Point p2)
{
    Double angleFromXAxis = Math.Atan ((p2.Y - p1.Y ) / (p2.X - p1.X ) ); // where y = m * x + K
    return  p2.X - p1.X < 0 ? m + Math.PI : m ); // The will go to the correct Quadrant
}

private Double NormalizeAngle(Double angle)
{
    return angle < 0 ? angle + 2 * Math.PI : angle; //This will make sure angle is [0..2PI]
}

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