CODEWITHSUNDEEP
javaalgorithmgeometrynanvertices
rikuoreo
rikuoreo

Reputation: 9

Access area from vertices of triangle

I'm attempting to write Java code that takes the vertices of a triangle (which will be user input) and outputs the area of said triangle. I'm getting NaN as a response. Should I be changing my types into floats? Am I taking a longer route to try and solve this problem?

Formulas used are Distance formula and Heron's formula.

import java.util.Scanner;

public class TriangleArea {

    public static void main(String[]args){

        Scanner user = new Scanner(System.in);

        System.out.println("To compute the area of a triangle, please input a point in a vertex when prompted");

        System.out.println("Please input X of the first vertex: x ");
        double firstVertexX = user.nextDouble();

        System.out.println("Please input Y of the first vertex: y ");
        double firstVertexY = user.nextDouble();        

        System.out.println("Please input X  of the second vertex: x");
        double secondVertexX = user.nextDouble();

        System.out.println("Please input Y of the second vertex: y ");
        double secondVertexY = user.nextDouble();       

        System.out.println("Please input X of the third vertex: x");
        double thirdVertexX = user.nextDouble();

        System.out.println("Please input Y of the third vertex: y");
        double thirdVertexY = user.nextDouble();        

        double sideOneX = Math.pow(firstVertexX * 1, 2) - Math.pow(secondVertexX * 2, 2);
        double sideOneY = Math.pow(firstVertexY * 1, 2) - Math.pow(secondVertexY * 2, 2);
        double sideOne = Math.pow(sideOneX + sideOneY, .5);

        double sideTwoX = Math.pow(secondVertexX * 1, 2) - Math.pow(thirdVertexX * 2, 2);
        double sideTwoY = Math.pow(secondVertexY * 1, 2) - Math.pow(thirdVertexY * 2, 2);
        double sideTwo = Math.pow(sideTwoX + sideTwoY, .5);

        double sideThreeX = Math.pow(thirdVertexX * 1, 2) - Math.pow(firstVertexX * 2, 2);
        double sideThreeY = Math.pow(thirdVertexY * 1, 2) - Math.pow(firstVertexY * 2, 2);
        double sideThree = Math.pow(sideThreeX + sideThreeY, .5);

        double s = (sideOne + sideTwo + sideThree)/2;

        double areaStepOne = (s - sideOne) * (s - sideTwo) * (s - sideThree);
        double areaStepTwo = s * areaStepOne;
        double area = Math.pow(areaStepTwo, .5);

        System.out.println("The area of the triangle is " + area + ".");

        System.out.println("The area of the triangle is " + area);

    }
}

Upvotes: 0

Views: 535

Answers (2)

user1196549
user1196549

Reputation:

I advise you to use the simpler analytic formula

|(X2 - X0) (Y1 - Y0) - (X1 - X0) (Y2 - Y0)| / 2

Not taking the absolute value, the sign tells you if the triangle is clockwise or counterclockwise.

Upvotes: 1

halfflat
halfflat

Reputation: 1584

The issue is a miscalculation.

The length of a line segment from (x1,y1) to (x2,y2) is sqrt( (x1-x2)^2 + (y1-y2)^2 ).

What you are calculating instead is: sqrt( x1^2 - (x2*2)^2 + y1^2 - (y2*2)^2 ). And this can be negative, giving you the NaNs.

I'd change the lines to be like:

double sideOneX = firstVertexX - secondVertexX;
double sideOneY = firstVertexY - secondVertexY;
double sideOne = Math.sqrt(sideOneX * sideOneX + sideOneY * sideOneY);

(You can just use Math.sqrt(v) instead of Math.pow(v, .5).)

Upvotes: 1

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