Chief Delphi - Angle from X,Y

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- - Angle from X,Y (http://www.chiefdelphi.com/forums/showthread.php?t=27685)

Re: Angle from X,Y

It was a joke. The prize: Absolutely nothing!

Basically, I'm asking if anyone knows why you would want it on the controller.

Here is my Arc Tangent code:

Code:

#define ATAN_COUNT 64

char rom ATAN_ARRAY[64] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 

17, 18, 19, 21, 22, 23, 25, 26, 27, 29, 30, 32, 34, 

36, 37, 39, 41, 43, 46, 48, 50, 53, 56, 59, 62, 66, 

69, 74, 78, 83, 88, 95, 101, 109, 118, 128, 140, 154, 

171, 192, 218, 253, 299, 367, 473, 663, 1106, 3319};



char atan (char Num)

{

        char Index = 0;

        char Value = 0;

        char IsDone = 0;

        

        LOOP:

                if (ATAN_ARRAY[Index] > Num)

                        Value--;

                if (ATAN_ARRAY[Index] >= Num)

                        IsDone = 255;

                else if (Index >= ATAN_COUNT - 1) //was ATAN_COUNT + 1

                {

                        IsDone = 255;

                        Value = 64;

                }

                

                if (IsDone)

                        goto LOOP_DONE;

                else

                { Value++; Index++; }

                goto LOOP;

        LOOP_DONE:

        

        return Value;

}

The lookup table is compressed. If I were to use a regular variety than it would be 3320 elements long! Instead, I put the location of the element that the value changes. That's why I loop. I think this will work, but I'm not sure.

[edit]that chould be ATAN_COUNT - 1 not ATAN_COUNT + 1 at line 19[/edit]

Re: Angle from X,Y

hmmm you can also use vectors, and find the angle with the formula (u * v)/(|u||v|) (the dot product of u and v divided by the product of the magnitudes). This is useful if you are already using vectors, which are probably better suited for motion and such anyways.

Re: Angle from X,Y

Quote:

Originally Posted by scottm87

The result of that equation gives you the cos of the angle between the vectors. That is cos(x). You would still need to use an inverse trig function to find the angle (x).

I'm going to have to go ahead and give you -15 points for that one. o_O

-Daniel