Marijan Grgić

Empirical Research of Interpolation Methods in Distortion Modeling for the Coordinate Transformation between Local and Global Geodetic Datums

Conformal coordinate transformations very often are not accurate enough to be used for the coordinate transformations between local and global geodetic datums because of the inhomogeneity of the spatial data in different geodetic datums. Therefore, distortion modeling is used to improve the accuracy of the coordinate transformations. This paper presents empirical research on distortion modeling methods used to improve the coordinate transformation process from local to global geodetic datum and vice versa. Various models of distortion shifts in different grid resolutions were computed, evaluated, and compared with the official Croatian model of distortion shifts. Tested modeling methods are inverse distance to a power, kriging, minimum curvature, modified Shepard’s method, natural neighbor, nearest neighbor, polynomial regression, radial basis function, triangulation with linear interpolation, moving average, local polynomial, and least-squares collocation. Distortion model performance was evaluated using summary statistics derived from the back-interpolation for the independent control spatial data set. The present paper proposes the most appropriate method(s) of distortion modeling for the Croatian case and gives brief instructions on possible coordinate transformation improvements of the official Croatian coordinate transformation.

Empirical comparison of the Geodetic Coordinate Transformation Models: a case study of Croatia

This paper presents empirical research on coordinate transformation models that enable coordinate transformations between the historical astro-geodetic datums and datums related to the European Terrestrial Reference System (ETRS), through a case study of the Republic of Croatia. Thirteen models were investigated for the transformation from the historical Croatian State Coordinate System (HDKS) to the Croatian Terrestrial Reference System (HTRS96): Molodensky 3 and 5 parameter (standard and abridged) conformal transformation models, 7 parameter transformation models (Bursa-Wolf and Molodensky-Badekas model), Affine transformation models (8, 9, 12 parameter), Multiple Regression Equation approach, and several transformation models that include extending of the aforementioned 7 parameter and 8, 9, 12 parameter Affine transformation models with distortion modelling. Most of the models were investigated for the first time over the Croatian territory. Analysis of transformation models performance was conducted using an independent data set of reliable geodetic points. The study provides mutual comparison of the models and their comparison with the official Croatian transformation model called T7D. Furthermore, the most appropriate transformation model(s) were defined regarding the required accuracy and the available resources for the coordinate transformation models implementation. In addition, the paper provides a brief theoretical background and equations of each transformation model and summarises the bibliography on the research topic.

Absolute Sea Level Surface Modeling for the Mediterranean from Satellite Altimeter and Tide Gauge Measurements

ABSTRACT Changes in the height of the ocean can be described through the relative and absolute sea level changes depending on the geodetic reference the sea level records are related to. Satellite altimetry provides absolute sea level (ASL) measurements related to the global geodetic reference, whereas tide gauges provide relative sea level (RSL) measurements related to the adjacent land. This study aims at computing the ASL surfaces for different time epochs from combined satellite altimeter and tide gauge records. A method of sea level data fusion is proposed to enable modeling of the impact of present and future sea level changes on the coast. Sea surface modeling was investigated for ten different gridding methods commonly used for the interpolation of altimeter data over the open ocean and extrapolation over the coastal zones. The performance of gridding methods was assessed based on the comparison of the gridded altimeter data and corrected tide gauge measurements. Finally, the sea level surfaces related to the GRS80 global reference ellipsoid were computed for the Mediterranean Sea over the altimeter period. In addition, the current sea level trends were estimated from both sea level measurements.