The ColRLSC-IAPG2019 gravimetric geoid has been computed by the Institute of Astronomical and Physical Geodesy, Technical University of Munich. It has been worked out in the frame of the International Association of Geodesy Joint Working Group 2.2.2 "The 1 cm geoid experiment" and the so called "Colorado experiment". The area covered by the model is 251°E ≤ longitude ≤ 257°E, 36°N ≤ latitude ≤ 39°N with a grid spacing of 1' in both latitude and in longitude. Input data include terrestrial and airborne gravity observations, the latter being filtered for the reduction of high-frequency noise.

The computation is based on the remove-compute-restore technique with XGM2018 as global geopotential and Earth2014 / ERTM2160 for the topographic gravity effects. Height anomalies are calculated by a one-step Residual Least-Squares Collocation (RLSC, Willberg et al. 2019), also including full covariance information from the high-resolution global geopotential model. The classical formula by Heiskanen and Moritz (1967) is used for the geoid/quasi-geoid separation. This conversion is based on strong simplifications and has been computed only for the purpose of the "Colorado experiment", since the ColRLSC-IAPG2019 solution is mainly focussed on the quasi-geoid computation. The accuracy of the geoid model, when compared against GSVS17 GPS/leveling, is equal to 3.1 cm.

The quasi-geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.

The International Service for the Geoid (ISG) was founded in 1992 (as International Geoid Service - IGeS) and it is now an official service of the International Association of Geodesy (IAG), under the umbrella of the International Gravity Field Service (IGFS). The main activities of ISG consist in collecting, analysing and redistributing local and regional geoid models, as well as organizing international schools on the geoid determination (Reguzzoni et al., 2021).