[BUG] 4.10.1 Wrong value with float

[anonymous_user_b2d0389d]

Hi ,

I’m working on camera movement for my character since 3 week and i always have issue with rotation value …

So today i decided to redo the entire code and i found that UE4 give me wrong value .

Explanation :

On begin play i get the rotation of my character :
(i call a function but i show what it does few lines later don’t worry )

Then i check this rotation and depending of the value i set it to 0.0 , 90.0, 180.0, or 270.0 :

After that i set a rotator variable to store this rotation (i use this rotation as a default rotation ):

Then i call a function i’ve made to be sure that my rotation (on yaw) is between 0 and 360 to get rid of negative value :

(what the function do : )

I set 4 rotator variable with 4 different value (for the 4 angles : 0 , 90 , 180 , 270) :
(i use collapsed node to get some space )
(as you can see i set the result in another rotator variable to use it later and dont risk to alterate the first one (char default clamp rot …))

Inside the collapsed node :

Then i set the world rotation of my mesh (my character mesh ) with the value (Default Rot … ) :

After that i have a piece of code who basically set the right rotation when i press the right key :

every tick (with a delay to avoid spam ) i print the value of the rotation of my mesh (world Rot ) and the value of the backward variable (charRotBW ) :

The result in play mode :
(the mesh world rotation is blue and the backward value is orange )

As you can see the actual mesh world Rotation is 0.0 (no problem ) and the backward world rotation is at 180.0 (here again no problem )
But look at this :

You see ? i have a variable with a yaw value of 180 , and when i set the world rotation of my mesh with this variable the value go from 180.0 to -179.9 … WTF !!? why 179.9 ? and why negative value ?

so yeah i’m done with it , i’ve almost lost 3 week of work and i don’t understand the value change .

all idea are welcome , if you need more info ask me

hope you guys can figure it out and thanks for your help and for taking your time to read me .

merry christmas and happy new year !

[anonymous_user_e660f14a]

I can tell you why it happens, but I’m not good enough at math to tell you how to fix it. It’s gimbal lock. Gimbal lock - Wikipedia https://www.youtube.com/watch?v=zc8b2Jo7mno

In robotics, gimbal lock is commonly referred to as “wrist flip”, due to the use of a “triple-roll wrist” in robotic arms, where three axes of the wrist, controlling yaw, pitch, and roll, all pass through a common point.

An example of a wrist flip, also called a wrist singularity, is when the path through which the robot is traveling causes the first and third axes of the robot’s wrist to line up. The second wrist axis then attempts to spin 180° in zero time to maintain the orientation of the end effector. The result of a singularity can be quite dramatic and can have adverse effects on the robot arm, the end effector, and the process.

And it’s changing to 179.999985 because of floating point errors. Nothing really to worry about there.

On the other hand, your code to round the rotation to 90° is excessive, just do this or use the “Snap To Grid (float)” node.

[anonymous_user_b2d0389d]

Hi ,

Thank you a lot for your answer ! i now understand why Unity is using Quaternion

I’ll try the use of Snap To grid and this afternoon and came back with the result hope it work and again : thank you for your help !