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c#mathangleatan2

Shifting angles while using Atan2

I am currently using Atan2 to calculate the player heading angle.

however after some trial and error I discovered that the in-game angle's are rather different to that of a "normal" lay out :

enter image description here

        ReturnedAngle = Math.Atan2(Y2 - Y1, X2 - X1);  /// ArcTan2 the difference in our Y axis is always passed first followed by X

        ReturnedAngle = (180 / Math.PI) * ReturnedAngle; /// Converting our radians to Degrees the convervion ends at 358 not the full 360 degrees.

        ReturnedAngle = Math.Round(ReturnedAngle + 360, MidpointRounding.AwayFromZero) % 360; /// MOD and round our angle.

Above is the C# code I am using to calc the heading angle. My questions is how would I go about converting this angle from the "normal" angle system to the in-game one.

Solution

  • I think this is your situation. You have a right-hand coordinate system, but you are measuring a clock-wise angle, which is inconsistent.

    In any case, draw a small positive angle from 360 (red below) to form a right triangle (purple below) with positive sides.

    fig1

    To measure the angle θ of the triangle, measure the short side Δx and the long side Δy and compute.

    var θ = Math.Atan2(Δx, Δy);

    This would work for any positive or negative values for the two sides. For example, if the angle goes above 90° then Δy would flip signs, as your target point is going to be below the origin. But the beauty of Atan2() is that you don't need to worry about these cases as it works on all four quadrants if you make it work for a small positive angle.

    In reverse you have

    var Δx = R*Math.Sin(Θ);
var Δy = R*Math.Cos(Θ);

    where R is the distance between the target and the reference point.