Code

private void AlignRotatedNodes(
	ShapeNode anchorNode, float nX, float nY,
	ShapeNode attachNode, float tX, float tY)
{
	// the absolute coordinates of the anchor node alignment point
	RectangleF anchorRect = anchorNode.Bounds;
	Matrix t = new Matrix();
	PointF c = new PointF(
		anchorRect.X + anchorRect.Width / 2,
		anchorRect.Y + anchorRect.Height / 2);
	t.RotateAt(anchorNode.RotationAngle, c);
	PointF[] n = new PointF[] { new PointF(
		anchorRect.X + nX * anchorRect.Width,
		anchorRect.Y + nY * anchorRect.Height) };
	t.TransformPoints(n);
	float nx = n[0].X;
	float ny = n[0].Y;

	// the absolute coordinates of the attached node alignment point
	RectangleF attachRect = attachNode.Bounds;
	float tx = attachRect.X + tX * attachRect.Width;
	float ty = attachRect.Y + tY * attachRect.Height;

	// this transform moves and rotates the attached node to align the specified points
	Matrix m = new Matrix();
	m.RotateAt(anchorNode.RotationAngle, new PointF(tx, ty));
	m.Translate(nx - tx, ny - ty, MatrixOrder.Append);

	// find the new position of the attached node center
	float cx = attachRect.X + attachRect.Width / 2;
	float cy = attachRect.Y + attachRect.Height / 2;
	PointF[] newCenterT = new PointF[] { new PointF(cx, cy) };
	m.TransformPoints(newCenterT);

	// move the node
	float newX = newCenterT[0].X - attachRect.Width / 2;
	float newY = newCenterT[0].Y - attachRect.Height / 2;
	attachNode.Move(newX, newY);
	attachNode.RotationAngle = anchorNode.RotationAngle;
}

ShapeNode n1 = diagram.Factory.CreateShapeNode(50, 50, 30, 40);
n1.RotationAngle = 120;
ShapeNode n2 = diagram.Factory.CreateShapeNode(130, 60, 20, 30);
AlignRotatedNodes(n1, 0, 0.5f, n2, 1, 0.5f);