Angle Measurer in C#

Question

I want to make a tool that can measure angles between two user defined spots on a form. I have no code to do this at the moment, so any code would be appreciated.

Thanks

UPDATE

It needs to be in Degrees and my points are 3 pictureboxes, each with different colours on each of the three points for the angle to be measured.

UPDATE

This is my new current code:

namespace Angle_Measurer_Tool
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();                
        }

        int Dotter = 0;

        private void button1_Click(object sender, EventArgs e)
        {
            Dotter = 1;
        }

        public int Distance2D(int x1, int y1, int x2, int y2)
        {    
            int result = 0;
            double part1 = Math.Pow((x2 - x1), 2);

            double part2 = Math.Pow((y2 - y1), 2);
            double underRadical = part1 + part2;
            result = (int)Math.Sqrt(underRadical);

            return result;
        }

        private void pictureBox1_MouseClick(object sender, MouseEventArgs e)
        {
            if (Dotter == 1)
            {
                dot1.Visible = true;
                dot1.Location = e.Location;
                Dotter = 2;
            }
            else if (Dotter == 2)
            {
                dot2.Visible = true;
                dot2.Location = e.Location;
                Dotter = 3;
            }
            else if (Dotter == 3)
            {
                dot3.Visible = true;
                dot3.Location = e.Location;
                Dotter = 4;
            }
            else if (Dotter == 4)
            {
                dot1.Visible = false;
                dot2.Visible = false;
                dot3.Visible = false;
                Dotter = 1;
            }

            anglesize.Text = Convert
                .ToInt32(Distance2D(
                             dot1.Location,
                             dot2.Location,
                             dot3.Location))
                .ToString();
        }
    }
}

and my problem is the line of actually putting the size of the angle in the label I have made called anglesize.

Answer 1

To find the angle formed by three points, you can use the dot product . Say you have the three points set up like this:

     dot1        
     /
  A /
   /
  / theta
dot2-------dot3
       B

I assume you want to find the angle theta between the lines created by points dot1 , dot2 and dot3 , where they're points that you've collected from the user. Then, you can define two vectors A and B :

A = dot1 - dot2
B = dot3 - dot2

Subtraction of two points simply means that you subtract each corresponding component. So it might look like this in code:

// I'll just use another point to represent a vector
Point A = new Point();
A.X = dot1.X - dot2.X;
A.Y = dot1.Y - dot2.Y;

Point B = new Point();
B.X = dot3.X - dot2.X;
B.Y = dot3.Y - dot2.Y;

The angle between these two vectors as defined by the dot product is:

                A * B
theta = acos(-----------)
             ||A|| ||B||

Where ||A|| and ||B|| are the lengths of the vectors A and B respectively, which is the square root of the sum of the squares of the components (which is simply the distance formula).

double ALen = Math.Sqrt( Math.Pow(A.X, 2) + Math.Pow(A.Y, 2) );
double BLen = Math.Sqrt( Math.Pow(B.X, 2) + Math.Pow(B.Y, 2) );

The dot product A * B is simply the sum of the products of the components, so it might look like this in code:

double dotProduct = A.X * B.X + A.Y * B.Y;

So you may perhaps have a dot product defined like this:

double theta = (180/Math.PI) * Math.Acos(dotProduct / (ALen * BLen));

This gives you the angle in degrees (remember that Math.Acos() returns the angle in radians).

Answer 2

similar to In silico's answer, you can use a combination of a dot product and cross product to get the angle, and not just the undirected angle.

where a and b are vectors run from the point you want to calculate the angle from to the corners of your picture boxes, respectively.

a*b = |a| |b| cos theta

axb = |a| |b| sin theta

axb / a*b = tan theta

atan2(axb, a*b) = theta

Answer 3

To measure an angle you need three points or a base direction.

Math.Atan2(y, x) can be used to measure the angle to the x-axis.

Note that y is the first param and not the second. Unlike other versions of this function it is safe with x=0

To transform the result which is given in radians to degrees you need to multiply with (180/Math.PI)

Answer 4

Hey this seems like a homework question so I won't answer directly but you can find something here:

http://msdn.microsoft.com/en-us/library/system.math.atan.aspx

Answer 5

总是有适当按摩过的atan2(dy2, dx2) - atan2(dy1, dx1) 。

Answer 6

First you need to measure the distance between your points:

    public int Distance2D(int x1, int y1, int x2, int y2)
    {

        int result = 0;
        double part1 = Math.Pow((x2 - x1), 2);

        double part2 = Math.Pow((y2 - y1), 2);
        double underRadical = part1 + part2;
        result = (int)Math.Sqrt(underRadical);

       return result;
  }