Explain triangulation in geodetic surveying.

Triangulation establishes horizontal control through a network of triangles where all angles and at least one base line are measured. Triangle vertices form control points. Procedure: select intervisible stations forming well-conditioned triangles (angles between 30-120 degrees), measure baseline with high precision, observe all angles with theodolite/total station using multiple rounds. Compute sides using sine rule. Adjust observations by method of least squares. Calculate coordinates. Primary triangulation covers country, secondary fills gaps, tertiary provides local control. Largely replaced by GPS but principles still relevant.