[RESOLVED] Finding an Angle

[L3mmy]

Hey, i was hoping to get some Help with Finding Angles between two Points, i have got the numbers moving a little with math.atan etc..

Like this:

(SEE ATTACHMENT)


The Grey Line from the Point in the Center to the Mouse Pointer is what i need to calculate. Numbers are as you see in the picture

Someone can help me out?..Endless and Pointless hours trying so far

- Cheers in Advanced.. L3mmy

[Shaggy Hiker]

Well, first you need the lengths of the sides of the triangle:

diffX = abs(X1-X2)
diffY = abs(Y1-Y2)

Now, the Tangent of the angle is equal to diffY (opposite side) / diffX (adjacent side). So if you take the ArcTan of (diffY/diffX), you will get a number that will be the angle in radians. To turn that into degrees, multiply by 180 and divide by pi. Thus, the whole equation looks like:

angle in degrees = (180 * Math.ATan(math.abs((Y1-Y2)/(X1-X2))))/3.1415

That will get you pretty close. A more accurate value for pi would give you more significant figures, but this will get you accurate to about three decimal places.

[L3mmy]

I don't seem to beable to get it working Could you show me a little Example..

[jmcilhinney]

How about you show us your attempt?

[L3mmy]

Don't Know what your Trying to Imply on me there but I'm not too Good at maths..or Angles..and here's what i got..It doesn't Return the Right Value..From the Center of the Form, to the Cursor Position.

Private Sub Form1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseMove
        
        Dim Angle As Double

        Angle = (180 * Math.Atan(Math.Abs((Cursor.Position.Y - Me.Height / 2) / (Cursor.Position.X - Me.Width / 2)))) / 3.1415

        Label2.Text = Angle

End Sub

[jmcilhinney]

You need to be aware that the positive Y direction on your form is downwards, where your calculations are assuming that it's upwards.

You should also be aware that the middle of the form's client area, which excludes the border and title bar, would be found using the ClientSize, not the Height and Width.

You should also be using the Math.PI constant to convert radians to degrees.

[jmcilhinney]

Another point to note, which I forgot to mention, is that Cursor.Position is in screen coordinates, not form coordinates.

I would suggest that you start off by making sure you can calculate the correct opposite and adjacent values before you worry about anything else. ALWAYS break your problem down and solve the first bits first. The PointToClient method of your form will be useful.

[jmcilhinney]

You should also note that you're never going to get an angle outside the of 0-90 the way you're doing it. You'd have to use the signs of the opposite and adjacent sides specifically to determine which quadrant you're in.

[jmcilhinney]

Hmmm... I see that this thread is now resolved. It's customary to provide the final solution for those who may have the same question in future. It's also considered polite to tell people that the problem is solved and thanks for the help.

[Shaggy Hiker]

I would guess that a combination of your post #6 and #8 solved the issue.

[L3mmy]

Sorry i didn't reply..I ended up asking a Friend on MSN..He let me use some Code of his..