Math.atan2 Function Explanation

[ARaza]

Hello guys
This is a piece of code from AS3 Making Things Move
I tried to understand what actually atan2 does?

Please explain

Hopefully, ill get help from here :)

Thanks in advance

[Ned Murphy]

If this is a trigonometry wondering, you can look up atan2 via Google and try to find an explanation that makes sense to you (it can be hard to explain in simple terms by words alone). Here's a link to what Wikipedia has to say: http://en.wikipedia.org/wiki/Atan2

In the simplest of terms for the code shown, what it's doing is telling you the angle (in radians) of the mouse relative to the x and y location of an arrow (likely the axis of rotation).

[ARaza]

Thanks for your replies,
I tried to explain what i learnd from ur discussion
Please correct me if i am wrong

Due to u guys, i could learn these difficult things

Thanks once again :)

[ARaza]

Many Thanks :)
Pretty bad with Math
so u have to tolerate me for a while.


I mean, how dy and dx forms a triangle? are not they at the same point :/
this is where im struck !
can u jst visualize this things in words?

[Ned Murphy]

I'm no math expert either, so if I'm off in this attempt, a more accurate description is welcome. The part I won't be able to explain is the atan2 bit itself.

If you look at dx and dy, they are not points, but the distance between two points. So you have an x-related distance of dx, and a y-related distance dy (the "d" is also often referred to as "delta", or "the change in").

When you take the x-length and intersect it with the y-length, you end up with a right angle. The rest is where I best not tread trying to explain, just accept that the atan2 relates to those lengths, possibly providing the angle of a line that would join them from the 0,0 axis to the opposite corner were you to make a rectangle of it.

While I prefer to not drop names, there is one person I can think of in these forums that likely understands this like we understand tomorrow is Sunday. Maybe he'll stop in and give it a shot.

[kglad · Accepted solution]

that's pretty accurate.

if you remember from trigonometry, the tangent of an angle (theta) formed by the x-axis and a line from (0,0) to (x,y) is y/x. ie, tan(theta) = y/x.

and the arctan is just the inverse: given the number y/x, what's the angle? ie, arctan(y/x) = theta.

in mos' code (dx,dy) can be considered a point on a cartesian coordinate system. if you draw a line from the (0,0) to (dx,dy) that line intersects the x-axis and forms an angle with the x-axis. that angle is the inverse tangent (arctan) of dy divided by dx (dy/dx).

flash, in addition to having a Math.atan(y/x) function also has an atan2 function Math.atan2(y,x) that accepts two parameters so no division is needed.

[Ned Murphy]

Thanks for stopping in... I was hoping you might. If I remembered much of anything from trig, I might have stood a chance at providing the proper explanation, but I'd still probably have to blow the dust off some old textbooks.

[ARaza]

Sorry, these right side of the monitor got messed (containing = symbols)
but else is quite clear.
Thanks in advance

[kglad]

no.

the x-axis is a horizontal line that runs through the origin (0,0).

draw a line from 0,0 to Mx,My
draw a line from 0,Mx to Mx,My

that forms the relevant triangle. the relevant angle is the angle formed by the line from 0,0 to Mx,My and the x-axis.

[ARaza]

Is this right now?

[ARaza]

@kglad
Please Confirm it
As i cant trust on my personal judgment !
Thanks

[kglad]

1- looks ok

2- looks more like a line from Mx,0 to Mx,My

[ARaza]

Thanks, ill come up with some sin cosin questions too
hopefully, ull help in those matters too 🙂

[kglad]

you're welcome,