Referentiepunten

Referentiepunten, or reference points, are fixed points whose position is known with high accuracy and which serve as a basis for measuring, mapping or orienting other data. They provide an origin, a scale, or a direction in space and are essential for achieving consistency between measurements taken at different times or with different instruments.

In surveying and geodesy, referentiepunten are often called control points or benchmarks. They define datums and supply tie-ins for local surveys to national or global coordinate systems. Their coordinates may be geographic (latitude, longitude, height) or projected (X, Y, Z). Measurements of unknown points are transformed using these references, enabling compatible maps and datasets. Global navigation satellite systems (GNSS) also use reference points to anchor positions in a network.

In other fields, reference points appear as fiducial markers or keypoints in image processing and computer vision, used to register or align images and 3D models. In cartography and navigation, they anchor maps to real locations and support height references such as water levels (for example NAP in the Netherlands) or other local datums.

Criteria for good referentiepunten include stability and permanence over time, distinctiveness to be unambiguous, accessibility for measurements, and a precisely known set of coordinates. They are usually maintained by national or regional surveying authorities and updated when the reference network is expanded or redefined.