General Discussion

I'm 20ish years removed from trig, so I've forgotten most of what I knew.

I've searched the net, but can't find a "simple" answer, everything I've found deals with problems more complicated than mine...

All I need to do is to be able to find the angle to a specific point on a grid.

For instance, the angle to (5, 5) is 45 degrees. I can do that.  acos(5 / sqrt(5*5 + 5*5)) / (2pi) * 360.

And the angle to (2, 20) is acos(2 / sqrt(2 * 2 + 20 * 20)) / (2pi) * 360 = 84 degrees.

But... my problem comes in when I want to find, say, (2, -20). I still come up with 84 degrees.

What am I overlooking (something with signs I'm sure)?

Thanks in advance.

2, -20 would still be 84 degrees from the x-axis.

You could find the 'actual' angle by

Degrees are always positive unless you've moved clockwise from the origin. So this point would be -84 degrees. or, if you were moving counterclockwise from origin, it would be 276 degrees (360-84)

There are four quadrants, and 2, -20 is in the fourth (the bottom right one).

So the only thing I can really do is just check the signs of the x and y coords to find the quadrant and work it from there? Poopy, I hate inelegant solutions like that :).

I wanted some clean way to come up with the 276 :).

I would prefer a clean way too, but the arccos has no negative range :(. (I think)

Originally posted by tylerthedrui

I would prefer a clean way too, but the arccos has no negative range :(. (I think)

Your using length to calculate angles.
The concept of a negative length is nonsensical, it purely defines direction (well thats my understanding in this highly excitable pre-greenbay game state)

Ah, to be young and work with numbers in math... *sigh* I guess it's back to practicing my sideways 8's.

Hehe, that's the problem, I'm not young anymore, and I've forgotten how to do the easy stuff LOL. I have a super fancy computer and a super fancy calculator, but I can barely remember how to do this stuff.

Originally posted by Nasica

Originally posted by tylerthedrui

I would prefer a clean way too, but the arccos has no negative range :(. (I think)

Your using length to calculate angles.
The concept of a negative length is nonsensical, it purely defines direction (well thats my understanding in this highly excitable pre-greenbay game state)

GB lost because we were calling stupid plays and trying to be heroes rather than jump on the fumble :'(

Originally posted by tylerthedrui

 

Originally posted by Nasica

Originally posted by tylerthedrui

I would prefer a clean way too, but the arccos has no negative range :(. (I think)

Your using length to calculate angles.
The concept of a negative length is nonsensical, it purely defines direction (well thats my understanding in this highly excitable pre-greenbay game state)

Wasn't talking about a negative length. Negative angles are measured clockwise from the origin.

 

GB lost because we were calling stupid plays and trying to be heroes rather than jump on the fumble :'(

My apologies, i actually didnt mean to quote you, but to quote the message above yours by the OP

  Remember, the Tangent of an angle is the opposite over the adjacent.  Divide the Y coordinate by the X coordinate, then take the inverse tangent of that number, and boom, you have the angle.  Its a joke, really, when you remember the method.