Code

PointF startPoint = new PointF();

private void diagram_NodeStartModifying(object sender, NodeValidationEventArgs e)
{
	startPoint = e.Node.GetCenter();
}

private void diagram_NodeModified(object sender, NodeEventArgs e)
{
	var currentPoint = e.Node.GetCenter();
	bool left = currentPoint.X < startPoint.X;
	bool right = currentPoint.X > startPoint.X;
	bool up = currentPoint.Y < startPoint.Y;
	bool down = currentPoint.Y > startPoint.Y;
}