Normal triangulation of a location is taken from 3 points of measurement determining a specific location from the distance measure from the 3 point on a 2D plain.
Quadrulation (Pyramidulation) of a location is to determine a 3D locations by adding an extra point higher up on the Z axis.
The forth point of measurement can be used just like triangulation between all points to find the central location on the X, Y and Z plain.
In normal triangulation three distances from three location can be mapped easily on pen and paper, because it is 2D plain. When you add a forth dimension in a higher axis on the Z plain, you are able to measure in a 3D area based on the distance of 4 locations.
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