How to check if a point is located inside a triangle using coordinates?

Question

Suppose a right triangle is placed in a plane as shown below. The right-angle point is placed at (0, 0), and the other two points are placed at (200, 0), and (0, 100). Write a program that prompts the user to enter a point with x- and y-coordinates and determines whether the point is inside the triangle.

    `String xInput, yInput;
    double x, y;
    xInput = JOptionPane.showInputDialog("Enter the x-coordinate of the point");
    yInput = JOptionPane.showInputDialog("Enter the y-coordinate of the point");
    x = Double.parseDouble(xInput);
    y = Double.parseDouble(yInput);
    if (x <= 200 && x >= 0 && y <= 100 && y >= 0) {
        if (y = roundup(x/2))
            System.out.print("The point is in the the triangle");
        else
            System.out.print("The point isn't in the triangle");
    }else
        System.out.print("The point isn't in the triangle");`

The output is an error in the second if saying that a double can't be a boolean

This is the figure for clarifications

Actually even `<=` to also include the triangle area and not just its border. — Nico Schertler, Sep 10 '19 at 00:48
Use the ceil method. As far as I know, roundup does not exist. Also, did you mean to use = or == in your second if statement? — K Man, Sep 10 '19 at 00:58
It was mainly the = that should be == but now they're telling me that the roundup is the problem so what other methods can I use?| — michelpro332, Sep 10 '19 at 01:11
What are the stipulations of the assignment. Can you use the Polygon class? — WJS, Sep 10 '19 at 02:27
if anyone has an alternative code that might work, please wright it down. — michelpro332, Sep 10 '19 at 07:29
Math, three vectors for triangle,sign of out-products. https://stackoverflow.com/questions/2049582/how-to-determine-if-a-point-is-in-a-2d-triangle — Joop Eggen, Sep 10 '19 at 08:36

score 0 · Accepted Answer · answered Sep 10 '19 at 08:35

Basically you have a linear formula that is y = 100 - x/2 where x is between 0 and 200 so we can create simple method for that

static double calculateY(double x) {
    return 100.0 - x / 2.0;
}

and then compare x against the boundaries and y against the formula

 if (x < 0 || x > 200 || y < 0) {
     System.out.print("The point isn't in the triangle");
 } else if ( y <= calculateY(x)) {
     System.out.print("The point is in the the triangle");
 } else
     System.out.print("The point isn't in the triangle");
 }

score 0 · Answer 2 · answered Mar 17 '22 at 12:25

0

Consider a triangle with vertices at (0, 0), (1, 0), and (0, 1). Write a program that asks the user for x and y coordinates and then outputs whether the point is inside the triangle, on the border of the triangle or outside the triangle.

answered Mar 17 '22 at 12:25

Leonard Tangi Ndipolifa

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How to check if a point is located inside a triangle using coordinates?

2 Answers2