group of multiple realizations of the same terrestrial or vertical reference system that, for approximate spatial referencing purposes, are not significantly different
Note 1 to entry: Datasets referenced to the different realizations within a datum ensemble may be merged without coordinate transformation.
Note 2 to entry: 'Approximate' is for users to define and typically is in the order of under 1 decimetre but may be up to 2 metres.
EXAMPLE WGS 84 as an undifferentiated group of realizations including WGS 84 (TRANSIT), WGS 84 (G730), WGS 84 (G873), WGS 84 (G1150), WGS 84 (G1674) and WGS 84 (G1762). At the surface of the Earth these have changed on average by 0.7 m between the TRANSIT and G730 realizations, a further 0.2 m between G730 and G873, 0.06 m between G873 and G1150, 0.2 m between G1150 and G1674 and 0.02 m between G1674 and G1762).
ORIGIN: ISO/TC 211 Glossary of Terms - English (last updated: 2020-06-02)