Trying to rotate 3D vector in java

Question

Im trying to find the components/head of a 3D vector with in java. I have a already got the x,y,z variables setup and the corresponding rotation variables. Using these variables and vector math, I want to find the components after they have been rotated. You can think the x,y,z variables as a vector being translated.

Using the math from this post: Rotating a Vector in 3D Space

I wrote some code that was supposed to calculate position based on that last post:

//Rotate Z
x = (( x * Math.cos(radz)) - (y * Math.sin(radz)));
y = (( x * Math.sin(radz)) + (y * Math.cos(radz)));
//Ignore Z ###############################################

//Rotate Y
x = (( x * Math.cos(rady)) - (z * Math.sin(rady)));
//Ignore Y ###############################################
z = (( x * Math.sin(rady)) + (z * Math.cos(rady)));

//Rotate X 
//Ignore X ###############################################
y = (( y * Math.cos(radx)) - (z * Math.sin(radx)));
z = (( y * Math.sin(radx)) + (z * Math.cos(radx)));

Where x, y and z are the positions that need to be changed and radx, rady and radz are the degrees of rotation in radians.

Using this code, if you set the variables like so:

double radx = Math.toRadians(0f);
double rady = Math.toRadians(90f);
double radz = Math.toRadians(0f);

double x = 1;
double y = 0;
double z = 0;

System.out.println(x + " " + y + " " + z);

It outputs: 6.123233995736766E-17 0.0 6.123233995736766E-17

Which im fairly sure isn't accurate. . .

What am I doing wrong with this code? Is there a easier way to find the head of a 3D vector java?

Also I do have the joml library, but it seems to have the same issue with the vec.rotateX method.

Duloren · Accepted Answer · 2017-10-18T23:10:16.423

0

You are updating your variables early. Try to:

//Rotate Z
double newX = (( x * Math.cos(radz)) - (y * Math.sin(radz)));
y = (( x * Math.sin(radz)) + (y * Math.cos(radz)));
//Ignore Z ###############################################

x = newX;

//Rotate Y
newX = (( x * Math.cos(rady)) + (z * Math.sin(rady)));
//Ignore Y ###############################################
z = (( x * -Math.sin(rady)) + (z * Math.cos(rady)));

x = newX;

//Rotate X 
//Ignore X ###############################################
double newY = (( y * Math.cos(radx)) - (z * Math.sin(radx)));
z = (( y * Math.sin(radx)) + (z * Math.cos(radx)));

y = newY;

edited Oct 18 '17 at 23:10

answered Oct 18 '17 at 05:43

Duloren

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Works for x, y and z individually. Also works for x+y, x+z but not y+z for some reason. Im looking into that now. If possible can you figure that one? Also cheers – Oct 18 '17 at 06:38
Not clear if sums aren't working. Please provide a example of input and desired output you are looking for. – Duloren Oct 18 '17 at 11:11
Radx is fine dont worry about it and rady + radz are also fine indifidually. However when changing rady+radz together it breaks for some reason. Note these inputs are in degrees, to be converted in the code. When having radx as 0, rady as 135 and radz as 135. The result should be about: 0.5 -0.70710677 0.5 When its actually: 0.5 -0.70710677 -0.5 – Oct 18 '17 at 20:56
If your familiar with vector math, the math is in the origional question. That is what this code is trying to replicate. – Oct 18 '17 at 21:01
Humm, there is a sign error in the second x update and first z update at your code. I fixed it in my answer in the last edit. Please refer to http://www.nh.cas.cz/people/lazar/celler/online_tools.php to realize the properly coordinates for a vector rotated by 135 degrees in z and than rotated 135 degrees in y. – Duloren Oct 18 '17 at 23:17

Trying to rotate 3D vector in java

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