Understanding coordinate reference systems, datums and transformations

Spatial professionals are required to deal with an increasingly wide range of positioning information obtained from various sources including terrestrial surveying, Global Navigation Satellite System (GNSS) observations and online GNSS processing services. These positions refer to a multitude of local, national and global datums. A clear understanding of the different coordinate reference systems and datums in use today and the appropriate transformations between these is therefore essential to ensure rigorous consideration of reference frame variations in order to produce high-quality outcomes in spatial data analysis tasks. This paper provides a compendium for spatial practitioners and Geographic Information System (GIS) users, reviewing the concepts and definitions of coordinate reference systems and datums, and outlining the practical procedures for coordinate transformations in relation to both horizontal and vertical datums.