Juzzz - 1 year ago 140

Java Question

I am working on showing a 3D model (IFC) in Java3D. I need to rotate the object with 2 vectors, a direction vector and a axis vector that are given by the IFC model.

But I can't figure out how to get the right angle.

Code:

`// Create vectors`

Vector3f directionVector = new Vector3f(dx, dy, dz);

Vector3f axisVector = new Vector3f(ax, ay, az);

//Calculate angle

float angle = axisVector.angle(directionVector);

//create AxisAngle4f

AxisAngle4f axisAngle = new AxisAngle4f(axisVector, angle);

The axisVector is always (0.0, 0.0, 1.0), so it needs to be rotated on the Z-axis

But when I calculate the angle it seems always 1.5707964 (90°):

`Example 1:`

dir: (-1.0, 0.0, 0.0)

axis: (0.0, 0.0, 1.0)

angle: 1.5707964 (90.00000250447816)

AA: (0.0, 0.0, 1.0, 1.5707964)

Example 2:

dir: (0.0, 1.0, 0.0)

axis: (0.0, 0.0, 1.0)

angle: 1.5707964 (90.00000250447816)

AA: (0.0, 0.0, 1.0, 1.5707964)

Example 3:

dir: (1.0, 0.0, 0.0)

axis: (0.0, 0.0, 1.0)

angle: 1.5707964 (90.00000250447816)

AA: (0.0, 0.0, 1.0, 1.5707964)

I know through testing that -1.0 means inverted so 180°.

Can some one help me understanding what I am doing wrong?

Documentation for the placement object (Direction and axis)

Screenshots of the results:

- Orange: are the floors
- Green: is the roof
- Red: is de rotation point
- Left: Side perspective
- Right: Top perspective
- The group of 3 slabs have direction direction (0.0, 1.0, 0.0)
- The group of 2 slabs have direction direction (1.0, 0.0, 0.0)
- Roof has direction: (-1.0, 0.0, 0.0)

I did the *2 test to simulate the 180° of -1.0. as you can see in the last example the roof is correctly drawn.

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Answer Source

You don't need the angle between the direction vector and the axis vector. Since your axis vector is always (0.0, 0.0, 1.0), you can define a constant vector of (1.0, 0.0, 0.0) to which you can compare the direction vector, i.e.:

```
// Create vectors
Vector3f directionVector = new Vector3f(dx, dy, dz);
Vector3f axisVector = new Vector3f(ax, ay, az);
Vector3f constantBaseVector = new Vector3f(1, 0, 0);
//Calculate angle
float angle = constantBaseVector.angle(directionVector);
//create AxisAngle4f
AxisAngle4f axisAngle = new AxisAngle4f(axisVector, angle);
```

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