Stablize a value in c++

Question

I have a variable which is a Modulus of Congruence x=y(mod 360),which means y varies from 0 - 360 and if the value is greater than 360 it again comes to 0. For example x=5 for y = 365 .

I wrote this function to stabilize y , so if the difference between x and previousx is greater than 5 then i get x otherwise previousx .

float stabilize(float x,float previous){

    if(fabs(x-previousx)<5)
    {
        return previousx;
    }
    else
    {
        return x;
    }

}

This works fine between 0 to 360 But this fails on the boundary condition of 360 and 0 .How can i stabilize the value when y is a value near 0 such as 0.3 and previous y is near 360 such as 359. So the difference calculated here is 359 - .3 = 358.7 . but i want it to be the modulo 360 difference which is 1.3 .

So you want the absolute value of the angle difference between `x` and `y`? — Mysticial, Aug 03 '12 at 09:55
Okay, now I'm very confused about what the question is. So you already have a difference, but you want to normalize it to something like `[0,360)`? Can you give us examples of your inputs and expected outputs? — Mysticial, Aug 03 '12 at 10:06
ok , the input is always mod 360 . For example the inputs to the function, x = 358 and previousx = 2 , i want the output to be previousx and if x = 356 and previousx = 3 i want the output to be 356 . — rajat, Aug 03 '12 at 10:09
The variables names might be creating the confusion , i have edited question to make the question more clearer . — rajat, Aug 03 '12 at 10:13
Oh okay, you're just trying to test if the angle between `x` and `previousx` is less than `5`. [My answer here](http://stackoverflow.com/a/11498248/922184) has an `angleDiff()` function that will give you the difference between any two angles. The result is normalized to `[-180, 180)`. So that might do what you want. — Mysticial, Aug 03 '12 at 10:22

ekholm · Accepted Answer · 2012-08-03T10:04:15.757

4

What about something like if(fabs(x-previousx)<5 || fabs(x-previousx)>355)? Given that the input data is mod 360, if the difference is big enough it means that both values are close enough to the border.

edited Aug 03 '12 at 10:04

answered Aug 03 '12 at 09:57

ekholm

2,543
18
18

I don't see a reason why this should not work . I will try it out , thanks . – rajat Aug 03 '12 at 10:06
You might consider using a "while" to make this approach correct for numbers above 720 and below 360... – danielschemmel Aug 03 '12 at 12:57
But in this question the input numbers are always between 0 and 360, so let's keep it simple – ekholm Aug 03 '12 at 13:41

score 1 · Answer 2 · answered Aug 03 '12 at 09:57

1

You could subtract the original numbers and take modulo 360 of the fabs(result):

for example:

359 - 720.3 = -361.3
fabs(-361.3) = 361.3
361.3 % 360 = 1.3

answered Aug 03 '12 at 09:57

user1157159

23
1
6

I have no way of getting the original numbers , i am using a external library for getting the angles . – rajat Aug 03 '12 at 10:01

Stablize a value in c++

2 Answers2