In WPF 3D, various transformations could be applied to an object. One particular problem that I occasionally run into is when I want to apply a rotation transformation to an object and rotate it around its own center and axes.

The way I do it is as follows. First I apply 3 identity RotateTransform3D‘s to the object with AxisAngleRotation3D‘s objects underneath: one for the X axis, one for the Y axis and one for the Z axis. Then whenever I want to rotate the object around a certain axis, I obtain the corresponding RotateTransform3D object, set its center according to the (possibly) translated center of the object, and apply the rotation angle to the underlying AxisAngleRotation3D object. Some code will make this more clear.

First apply the 3 identity transforms to the object:

Transform3DGroup transforms = new Transform3DGroup();
// Rotation around X
transforms.Children.Add(new RotateTransform3D(new AxisAngleRotation3D(new Vector3D(1, 0, 0), 0)));
// Rotation around Y 
transforms.Children.Add(new RotateTransform3D(new AxisAngleRotation3D(new Vector3D(0, 1, 0), 0)));
// Rotation around Z
transforms.Children.Add(new RotateTransform3D(new AxisAngleRotation3D(new Vector3D(0, 0, 1), 0))); 
// Translate transform (if required)
transforms.Children.Add(new TranslateTransform3D());
MyObject.Transform = transforms;

Let’s say the function SetRotation is to be used for setting the rotation of the object. It will work as follows:

public void SetRotation(double amountX, double amountY, double amountZ)
{
	// Suppose we have a function that gives us all the transforms
	// applied to this object
	Transform3DGroup transfomrs = GetTransforms();
	TranslateTransform3D translation = transforms.Children[3];
	// Suppose GetCenter() obtains the center point of an object
	// in Point3D format
	Point3D translatedCenter = translation.Transform(GetCenter());

	RotateTransform3D rotX = (transforms.Children[0] as RotateTransform3D);
	RotateTransform3D rotY = (transforms.Children[1] as RotateTransform3D);
	RotateTransform3D rotZ = (transforms.Children[2] as RotateTransform3D);

	// Set the center point of transformation to the translated center of the object
	rotX.CenterX = rotY.CenterX = rotZ.CenterX = translatedCenter.X;
	rotX.CenterY = rotY.CenterY = rotZ.CenterY = translatedCenter.Y;
	rotX.CenterZ = rotY.CenterZ = rotZ.CenterZ = translatedCenter.Z;

	// Apply the angle amounts
	(rotX.Rotation as AxisAngleRotation3D).Angle = amountX;
	(rotY.Rotation as AxisAngleRotation3D).Angle = amountY;
	(rotZ.Rotation as AxisAngleRotation3D).Angle = amountZ;
}