Transform angles that are -180 to +180 to angles that are in the 0-360 degree range?

I am implementing a vector coding technique in matlab using the atan2d(diff(y),diff(x)) function, but the results are from -180 to +180 and I would like to have a 0-360 range. I tried to input an if statement for angles < 0 to have 360 added to them, but I couldn't get it to work. It is possible that I just didn't write the statement correctly, but I would appreciate any tips or advice.

[dpb]

"It is possible that I just didn't write the statement correctly, but I would appreciate any tips or advice."

Well, it's a little tough to comment on what we can't see...what did you try?

[Kylie Davis]

Sorry about that. I tried: if x < 0 x = x+360 end

But the other difficulty I am having is that I have so many data sets that I need to apply that to. I have hip, knee, and ankle joint angle data for both limbs of 18 subjects. So I need to have an if statement correcting the negative angles for 36 different sets.

Answer 1

[Star Strider]

This is my little anonymous function that I use for such problems:

Angles360 = @(a) rem(360+a, 360);                        % For ‘atan2d’

[Kylie Davis]

Again, sorry for my lack of knowledge... but do I only have to write this once at the end of the script or does it need to be written for every data set (i.e. for each individual subject's calculations). I tried to write it in at the beginning of the script but I saw no difference in my final plots. Thank you for all your help.

[Kylie Davis]

I think I got it to work. Thanks so much!

[Star Strider]

My pleasure!

It’s an anonymous function, and works like any other function. Just put it at the beginning of your code, then call it as:

Angles360 = @(a) rem(360+a, 360);                        % For ‘atan2d’
x = randi(9, 5, 1);                                 % Create Data
y = randi(9, 5, 1);                                 % Create Data
theta = atan2d(diff(y),diff(x));
theta360 = Angles360(theta);

Answer 2

[theodore panagos]

A formula to calculate an angle counter clockwise from x positive to 360 degrees:

f(x,y)=180-90*(1+sign(x))* (1-sign(y^2))-45*(2+sign(x)*sign(y)

-180/pi()*sign(x*y)*atan((abs(x)-abs(y))/(absx)+abs(y)))