Matej Varga

Accuracy validation and comparison of global digital elevation models over Croatia

Accuracy assessment of digital elevation models (DEMs) plays an important role in facing their use in geoscience applications. This study investigates the vertical accuracy of most recently published versions of global DEMs over Croatia: 1 arc-minute global relief model (ETOPO1), Global 30 Arc-Second Elevation (GTOPO30), SRTM30+, Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010), Altimeter Corrected Elevations 2 DEM (ACE2 DEM), Shuttle Radar Topography Mission GDEM (SRTM GDEM), and Advanced Spaceborne Thermal Emission and Reflection GDEM (ASTER GDEM). Geodetic ground control points (benchmarks) allowed the comparison in terms of vertical accuracy. Additionally, the differences between models in the identical points were determined and analysed after adjusting the models to the same resolution. The results have yielded information about the overall accuracy of models; the accuracy depending on height, land cover, and slope; presence of large and systematic errors; and mutual agreement between the models. Overall vertical accuracies according to the root mean square error over Croatia are: ETOPO1 27.6 m, GTOPO30 21.6 m, SRTM30+ 21.3 m, GMTED2010 7.4 m, ACE2 DEM 4.5 m, SRTM GDEM 3.8 m, and ASTER GDEM 7.1 m. The highest accuracy was shown by SRTM GDEM version 3, which is far better than the previously released versions. All models have proved to be worse in the rough and forest areas, whereas in flat and barelands, new-generation global DEMs SRTM GDEM, and ASTER GDEM are highly accurate.

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.

Models of geomorphometric parameters and drainage networks for the territory of Republic of Croatia

Models of geomorphometric parameters and drainage networks are widely used in many scientific and civilian branches and activities. They are created using the Earth’s land surface data, which are today mostly represented by digital elevation models (DEMs). The main objective of this study is to create models of slope, aspect, and drainage networks for the first time for the entire continental part of the Republic of Croatia, using the most detailed DEMs. In this paper, developed models are described, compared, and analysed, giving insights into morphological characteristics and structures of topographic surface. The quality of the derived models has been validated using existing independent data. Furthermore, because models were derived using various global DEMs, the differences between output models have been addressed and studied. Drainage network models were further analysed depending on several available computation algorithms (single and multiple flow direction) and threshold values. The analysis of the sensitivity and influence of input parameters and models on output models has been assessed in order to create reliable drainage network models for the future for other local or regional areas. Modeli geomorfometrijskih parametara i drenažne mreže imaju siroku primjenu u mnogim znanstvenim i civilnim granama i aktivnostima. Izrađuju se iz podataka o Zemljinoj povrsini koji su najcesce objavljeni u obliku digitalnih modela reljefa (DMR). Glavni je cilj ovoga rada izraditi modele nagiba, smjera nagiba i drenažnih mreža za kontinentalno podrucje Republike Hrvatske koristenjem najdetaljnijega globalnog digitalnog modela reljefa. Izrađeni modeli su opisani, uspoređeni i analizirani te daju uvid u morfoloske oblike i strukture topografske povrsine. Kvaliteta modela provjerena je na postojecim neovisnim podacima. Osim toga, s obzirom na to da su modeli izrađeni koristenjem razlicitih globalnih digitalnih modela reljefa, analizirane su razlike između izlaznih modela. Modeli drenažne mreže dodatno su analizirani ovisno o koristenim algoritmima (jednosmjerni i visesmjerni protok) i granicnim vrijednostima. Analiza osjetljivosti i utjecaja ulaznih parametara i modela na izrađene modele bit ce korisna za izradu pouzdanijih buducih modela drenažnih mreža za druga lokalna i regionalna podrucja.