The GEOID-MACAS2021 model for the urban area of the Macas City in Ecuadorian Amazon was computed with a non-conventional technique, such as Cokriging (Goovaerts, 1997), through the combination of GPS data/differential leveling and a densely sampled auxiliary variable. The GPS satellite positioning was performed using the Static Differential method through dual-frequency receivers in each point; regarding the level heights they were obtained by first-order differential leveling and the GPS leveling technique. A total of 17 geoid undulation data were used for the computation, while the geoid undulation from the EGM2008 model with a spatial resolution of 1 arc-min was proposed as an auxiliary variable for the interpolation (Odera & Fukuda, 2015). The ordinary Cokriging predictor was used for the study. In order to check the fit of the resulting geoid model, a cross-validation was carried out using the “leave one out” principle, obtained an RMSE of 5.3 cm. In addition, a validation was performed with external GPS/leveling data, reaching an accuracy of 2.1 cm RMSE. This model presents auspicious results for engineering applications, for obtaining level heights quickly and accurately.

The 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).