Angle between a Pair of Lines in 3D

Given coordinates of three points A(x1, y1, z1), B(x2, y2, z2), and C(x3, y3, z3) in a 3D plane, where B is the intersection point of line AB and BC, the task is to find the angle between lines AB and BC.

Examples:

Input: x1 = 1, y1 = 3, z1 = 3; x2 = 3, y2 = 4, z2 = 5; x3 = 5, y3 = 6, z3 = 9; 
Output: 54.6065
Input: x1 = 10, y1 = 10, z1 = 10; x2 = 0, y2 = 0, z2 = 0; x3 = 15, y3 = 10, z3 = 15; 
Output: 56.4496  

Approach:

1. Find the equation of lines AB and BC with the given coordinates in terms of direction ratios as: 

AB = (x1 – x2)i + (y1 – y2)j + (z1 – z2)k 
BC = (x3 – x2)i + (y3 – y2)j + (z3 – z2)k 

2. Use the formula for cos ? for the two direction ratios of lines AB and BC to find the cosine of the angle between lines AB and BC as: 

where, 
AB.BC is the dot product of direction ratios AB and BC. 
|AB| is the magnitude of line AB 
|BC| is the magnitude of line BC 

3. Suppose there are two direction ratios: 

A = ai + bj + ck
B = xi + yj + zk

 then 

Dot Product(A.B) = a*x + b*y + c*z 
magnitude of A = |A| = 
magnitude of B = |B| = 

4. The cosine of the angle calculated gives the cosine value in radian. To find the angle multiply the cosine value by (180/?).

Below is the implementation of the above approach:

C++

// C++ program for the above approach

#include "bits/stdc++.h"
#define PI 3.14
using namespace std;

// Function to find the angle between
// the two lines
void calculateAngle(
    int x1, int y1, int z1,
    int x2, int y2, int z2,
    int x3, int y3, int z3)
{
    // Find direction ratio of line AB
    int ABx = x1 - x2;
    int ABy = y1 - y2;
    int ABz = z1 - z2;

    // Find direction ratio of line BC
    int BCx = x3 - x2;
    int BCy = y3 - y2;
    int BCz = z3 - z2;

    // Find the dotProduct
    // of lines AB & BC
    double dotProduct
        = ABx * BCx
          + ABy * BCy
          + ABz * BCz;

    // Find magnitude of
    // line AB and BC
    double magnitudeAB
        = ABx * ABx
          + ABy * ABy
          + ABz * ABz;
    double magnitudeBC
        = BCx * BCx
          + BCy * BCy
          + BCz * BCz;

    // Find the cosine of
    // the angle formed
    // by line AB and BC
    double angle = dotProduct;
    angle /= sqrt(
        magnitudeAB * magnitudeBC);

    // Find angle in radian
    angle = (angle * 180) / PI;

    // Print the angle
    cout << abs(angle) << endl;
}

// Driver Code
int main()
{

    // Given coordinates
    // Points A
    int x1 = 1, y1 = 3, z1 = 3;

    // Points B
    int x2 = 3, y2 = 4, z2 = 5;

    // Points C
    int x3 = 5, y3 = 6, z3 = 9;

    // Function Call
    calculateAngle(x1, y1, z1,
                   x2, y2, z2,
                   x3, y3, z3);

    return 0;
}

Java

// Java program for the above approach
import java.util.*;

class GFG{

// Function to find the angle
// between the two lines
static void calculateAngle(int x1, int y1, int z1,
                           int x2, int y2, int z2,
                           int x3, int y3, int z3)
{

    // Find direction ratio of line AB
    int ABx = x1 - x2;
    int ABy = y1 - y2;
    int ABz = z1 - z2;

    // Find direction ratio of line BC
    int BCx = x3 - x2;
    int BCy = y3 - y2;
    int BCz = z3 - z2;

    // Find the dotProduct
    // of lines AB & BC
    double dotProduct = ABx * BCx +
                        ABy * BCy +
                        ABz * BCz;

    // Find magnitude of
    // line AB and BC
    double magnitudeAB = ABx * ABx +
                         ABy * ABy +
                         ABz * ABz;
    double magnitudeBC = BCx * BCx +
                         BCy * BCy +
                         BCz * BCz;

    // Find the cosine of the
    // angle formed by line
    // AB and BC
    double angle = dotProduct;
    angle /= Math.sqrt(magnitudeAB * magnitudeBC);

    // Find angle in radian
    angle = (angle * 180) / 3.14;

    // Print the angle
    System.out.printf("%.4f", Math.abs(angle));
}

// Driver code
public static void main(String[] args)
{

    // Given coordinates
    // Points A
    int x1 = 1, y1 = 3, z1 = 3;

    // Points B
    int x2 = 3, y2 = 4, z2 = 5;

    // Points C
    int x3 = 5, y3 = 6, z3 = 9;

    // Function Call
    calculateAngle(x1, y1, z1,
                   x2, y2, z2,
                   x3, y3, z3);
}
}

// This code is contributed by offbeat

Python3

# Python3 program for the above approach
import math

# Function to find the angle
# between the two lines
def calculateAngle(x1, y1, z1,
                   x2, y2, z2,
                   x3, y3, z3):

    # Find direction ratio of line AB
    ABx = x1 - x2;
    ABy = y1 - y2;
    ABz = z1 - z2;

    # Find direction ratio of line BC
    BCx = x3 - x2;
    BCy = y3 - y2;
    BCz = z3 - z2;

    # Find the dotProduct
    # of lines AB & BC
    dotProduct = (ABx * BCx +
                  ABy * BCy +
                  ABz * BCz);

    # Find magnitude of
    # line AB and BC
    magnitudeAB = (ABx * ABx +
                   ABy * ABy +
                   ABz * ABz);
    magnitudeBC = (BCx * BCx +
                   BCy * BCy +
                   BCz * BCz);

    # Find the cosine of
    # the angle formed
    # by line AB and BC
    angle = dotProduct;
    angle /= math.sqrt(magnitudeAB *
                       magnitudeBC);

    # Find angle in radian
    angle = (angle * 180) / 3.14;

    # Print angle
    print(round(abs(angle), 4))

# Driver Code
if __name__=='__main__':

    # Given coordinates
    # Points A
    x1, y1, z1 = 1, 3, 3;

    # Points B
    x2, y2, z2 = 3, 4, 5;

    # Points C
    x3, y3, z3 = 5, 6, 9;

    # Function Call
    calculateAngle(x1, y1, z1,
                   x2, y2, z2,
                   x3, y3, z3);

# This code is contributed by AbhiThakur

C#

// C# program for the above approach
using System;
class GFG{

// Function to find the angle
// between the two lines
static void calculateAngle(int x1, int y1,
                           int z1, int x2,
                           int y2, int z2,
                           int x3, int y3,
                           int z3)
{

    // Find direction ratio of line AB
    int ABx = x1 - x2;
    int ABy = y1 - y2;
    int ABz = z1 - z2;

    // Find direction ratio of line BC
    int BCx = x3 - x2;
    int BCy = y3 - y2;
    int BCz = z3 - z2;

    // Find the dotProduct
    // of lines AB & BC
    double dotProduct = ABx * BCx +
                        ABy * BCy +
                        ABz * BCz;

    // Find magnitude of
    // line AB and BC
    double magnitudeAB = ABx * ABx +
                         ABy * ABy +
                         ABz * ABz;
    double magnitudeBC = BCx * BCx +
                         BCy * BCy +
                         BCz * BCz;

    // Find the cosine of the
    // angle formed by line
    // AB and BC
    double angle = dotProduct;
    angle /= Math.Sqrt(magnitudeAB *
                       magnitudeBC);

    // Find angle in radian
    angle = (angle * 180) / 3.14;

    // Print the angle
    Console.Write(String.Format("{0:F4}", Math.Abs(angle)));
}

// Driver code
public static void Main()
{

    // Given coordinates
    // Points A
    int x1 = 1, y1 = 3, z1 = 3;

    // Points B
    int x2 = 3, y2 = 4, z2 = 5;

    // Points C
    int x3 = 5, y3 = 6, z3 = 9;

    // Function Call
    calculateAngle(x1, y1, z1,
                   x2, y2, z2,
                   x3, y3, z3);
}
}

// This code is contributed by Code_Mech

Javascript

<script>


// Javascript program for the above approach

var PI = 3.14;

// Function to find the angle between
// the two lines
function calculateAngle(
    x1, y1, z1,
    x2, y2, z2,
    x3, y3, z3)
{
    // Find direction ratio of line AB
    var ABx = x1 - x2;
    var ABy = y1 - y2;
    var ABz = z1 - z2;

    // Find direction ratio of line BC
    var BCx = x3 - x2;
    var BCy = y3 - y2;
    var BCz = z3 - z2;

    // Find the dotProduct
    // of lines AB & BC
    var dotProduct
        = ABx * BCx
          + ABy * BCy
          + ABz * BCz;

    // Find magnitude of
    // line AB and BC
    var magnitudeAB
        = ABx * ABx
          + ABy * ABy
          + ABz * ABz;
    var magnitudeBC
        = BCx * BCx
          + BCy * BCy
          + BCz * BCz;

    // Find the cosine of
    // the angle formed
    // by line AB and BC
    var angle = dotProduct;
    angle /= Math.sqrt(
        magnitudeAB * magnitudeBC);

    // Find angle in radian
    angle = (angle * 180) / PI;

    // Print the angle
    document.write(Math.abs(angle).toFixed(4));
}

// Driver Code
// Given coordinates
// Points A
var x1 = 1, y1 = 3, z1 = 3;
// Points B
var x2 = 3, y2 = 4, z2 = 5;
// Points C
var x3 = 5, y3 = 6, z3 = 9;
// Function Call
calculateAngle(x1, y1, z1,
               x2, y2, z2,
               x3, y3, z3);


</script>

Output:

54.6065