Code

void Fit3D()
{
	diagramView3D.PointCameraTo(CenterPoint());
	while (!Fits())
	{
		MoveCameraForward(-1);
		diagramView3D.ResetProjection();
	}
}

bool Fits()
{
	foreach (DiagramNode node in diagram.Nodes)
	{
		Rectangle rect = diagramView3D.GetProjectionRect(node);
		if (!diagramView3D.ClientRectangle.Contains(rect))
			return false;
	}

	return true;
}

Point3D CenterPoint()
{
	if (diagram.Nodes.Count == 0)
		return new Point3D();

	Point3D center = new Point3D();
	foreach (DiagramNode node in diagram.Nodes)
	{
		Point3D p = (Point3D)node.LayoutTraits[View3D.Position];
		center.X += p.X;
		center.Y += p.Y;
		center.Z += p.Z;
	}
	center.X /= diagram.Nodes.Count;
	center.Y /= diagram.Nodes.Count;
	center.Z /= diagram.Nodes.Count;

	return center;
}

private void MoveCameraForward(float dz)
{
	Matrix3D cameraRotationMatrix = GetRotationMatrix();
	if (cameraRotationMatrix == null)
		return;

	Vector3D v = new Vector3D(0, 0, dz);
	Vector3D r = cameraRotationMatrix.Invert() * v;

	Point3D cameraPosition = diagramView3D.CameraPosition;
	cameraPosition.X += (float)r.X;
	cameraPosition.Y += (float)r.Y;
	cameraPosition.Z += (float)r.Z;
	diagramView3D.CameraPosition = cameraPosition;
}

Matrix3D GetRotationMatrix()
{
	Point3D cameraRotation = diagramView3D.CameraRotation;

	double[] t = new double[3];
	t[0] = (Math.PI / (180 / cameraRotation.X));
	t[1] = (Math.PI / (180 / cameraRotation.Y));
	t[2] = (Math.PI / (180 / cameraRotation.Z));

	return
		new Matrix3D(1, 0, 0, 0, Math.Cos(-t[0]), Math.Sin(-t[0]), 0, -Math.Sin(-t[0]), Math.Cos(-t[0])) *
		new Matrix3D(Math.Cos(-t[1]), 0, -Math.Sin(-t[1]), 0, 1, 0, Math.Sin(-t[1]), 0, Math.Cos(-t[1])) *
		new Matrix3D(Math.Cos(-t[2]), Math.Sin(-t[2]), 0, -Math.Sin(-t[2]), Math.Cos(-t[2]), 0, 0, 0, 1);
}