//Read new settings
try
{
    Double WValue = System.Convert.ToDouble(QuaternionWText.Text);
    Double XValue = System.Convert.ToDouble(QuaternionXText.Text);
    Double YValue = System.Convert.ToDouble(QuaternionYText.Text);
    Double ZValue = System.Convert.ToDouble(QuaternionZText.Text);

    endQuaternion = new Quaternion(XValue, YValue, ZValue, WValue);
}
catch
{
    MessageBox.Show("Set non-null values for the quaternion.");
}

myQuaternionRotation3D = new QuaternionRotation3D(endQuaternion);
myRotateTransform3D.Rotation = myQuaternionRotation3D;

//update matrix display
qrotationMatrix3D = myRotateTransform3D.Value;