3d vector calculation in WPF

Question

Hi .. I draw two spheres in 3d WPF which has points like Point3D(0,0,0) and Point3D(-1.0,1.0,2.0) with the radius is 0.10

Now i want to draw a Cylinder joining these spheres, the only thing i have for this is radius 0.02. I want to know how to calculate the 3d point, height, direction etc for this cylinder.

I tried by finding the midpoint btw sphere points, it's placing the cylinder in the middle of those two spheres but not in the right direction. I am trying to rotate using in the code below.

    Vector3D v1 = new Vector3D(0, 0, 0);
    Vector3D v2 = new Vector3D(1.0, -1.0, 2.0);

    Vector3D center = v1+ v2/2;
    Vector3D axis = Vector3D.CrossProduct(v1, v2);
    double angle = Vector3D.AngleBetween(v1, v2);
    AxisAngleRotation3D axisAngle = new AxisAngleRotation3D(axis, angle);
    RotateTransform3D myRotateTransform = new RotateTransform3D(axisAngle, center);
    center.X = myRotateTransform.CenterX;
    center.Y = myRotateTransform.CenterY;
    center.Z = myRotateTransform.CenterZ;

but the double angle = Vector3D.AngleBetween(v1, v2); ruselting NaN

It would be really nice, if someone could help in doing this. Thanks in advance.

Answer 1

You could simply use a RotateTransform3D to rotate the cylinder to the required direction.

You can apply the transform to one of two properties here is an explanation of the options

Answer 2

The direction you need is the vector between the centres of the spheres:

direction.x = sphere1.Center.x - sphere2.Center.x;
direction.y = sphere1.Center.y - sphere2.Center.y;
direction.x = sphere1.Center.z - sphere2.Center.z;

Then divide these by the length of the vector to get a unit vector:

double length = Math.Sqrt(direction.x * direction.x +
                          direction.y * direction.y +
                          direction.z * direction.z);

direction.x /= length;
direction.y /= length;
direction.z /= length;

Then you can use this to calculate your rotation matrix.