Finally, these topographic measurements are complemented by topographic expeditious
methods such as plumb lines. The plumb lines must drop in a perfect vertical line and
should be suspended from any projecting element of the walls of the building. To achieve this,
some auxiliary elements might be required in the joint with the wall in order to ensure
that no contact between them takes place. The direction of the plumb line defines the direction
of the z-axis in the reference coordinate system and thus a check for possible out of plumb
could be done