Geodetski Institute Slovenije

Ljubljana, Slovenia

Geodetski Institute Slovenije

Ljubljana, Slovenia
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Cekada M.T.,Geodetski Institute Slovenije
Geografski Obzornik | Year: 2015

200 years from Tambora eruption - the last advance of Little Ice Age: Consequences testified in Slovenian oral tradition from Solĉava Glaciers advanced during the Little Ice Age until the year 1850. Last decade of this quite long period of cold weather, very favourable for the growth of glaciers, can be attributed to two volcanic eruptions in 1809 and 1815. The last eruption of the volcano Tambora, has caused "year without a summer" in 1816 and further two more years of distinctly bad weather, which caused widespread famine in the world. This famine also affected the population of Slovenia, as it is documented in the records of Joža Vršnik from the Solĉava Region. In 1810 the famine around Solĉava was supposedly so severe that people were dying from it.


Cekada M.T.,Geodetski Institute Slovenije | Lavric M.,Segova vas 11 | Fras M.K.,University of Ljubljana
Geodetski Vestnik | Year: 2017

Aerial laser scanning provides information about the reflectivity of the surface from which the laser beam was reflected; this information is given as an intensity of a laser point. By comparing the average non-normalised intensity values for different tree species growing in Slovenia in laser scanning data sets acquired with different wavelengths, whether tree species can be separated based only on laser scanning intensity data was investigated. We studied 113 single trees (57 coniferous and 56 deciduous trees), identified in the field and in four laser data sets. The first two were acquired in the 1550 nm wavelength: the first set in spring (May 15, 2012), the second in late summer (September 18, 2012). The last two sets were acquired in the 1064 nm wavelength: the third in winter (March 5, 2013) and the fourth in summer (July 7, 2014). Among other things, we have determined, the same as researchers before us: (i) that the average intensities of deciduous trees in both wavelengths are higher in the leaf-on season, while it is the opposite in the leaf-off season; (ii) that the average intensities of the combined class of first and the only reflections is higher than the average intensities of all reflections in leaf-on season; during the leaf-off season it is the opposite. The behavior of tree species Juglans regia, Acer Pseudoplatanus, Fraxinus excelsior and Tilia cordata (or Tilia Platyphylolos) also implies that the differences in the average intensities in laser time series enable the determination of the phenological phase of deciduous trees in the spring. © 2017, Zvava Geodetov Slovenije. All rights reserved.


The Slovenian national orthophoto in the scale 1:5,000 is made from the Cyclical Aerophotogrammetric Survey of Slovenia (CAS) images and the digital terrain model (DTM). It is the most widely used spatial source for a variety of GIS analyses and visual photointerpretation in Slovenia. Different vector or raster spatial layers can be shown on it, which may be even more precise than the orthophoto. The users of the orthophoto are often not aware, that orthophoto may include positional errors. Using the geometrical connection between the original image and the orthophoto we derive the maximal radial displacement expected on orthophoto for objects of different height above or below the DTM. We show that radial displacement of higher objects, like higher rocky cliffs (height 50 m), tall buildings (like church towers) and forest edge, may exceed the permitted positional error of the orthophoto, at least in the extreme cases when these objects are located near the seam lines of the orthophoto. We also mention orthophotos made from images of unmanned aerial vehicles (drones), where the problem of its positional accuracy is even broader, as for their production the DTM with nonuniform vertical accuracy is used. © 2016, Association of Slovenian Geographers. All rights reserved.


Cekada M.T.,Geodetski Institute Slovenije
Geografski Obzornik | Year: 2016

Nationwide aerial laser scanning of Slovenia was carried out mainly in period 2014-2015, two scanning blocks already in 2011. Products of laser scanning are: classified point cloud, the ground point cloud and digital terrain model. Data are intended for general cartographic representations in scales not more detailed than in scale 1:5000. The data were provided for 3D data acquisition of hydrography and water land use for total Slovenian area. They are also used for data acquisition of the topographic maps in scale 1:5000 and for making of national ortophotos within the Cyclical Aerial Survey (CAS) frame from 2015 on. The data enables study of the terrain under the vegetation in such details, that previously could be studied only by field work.


Mongus D.,University of Maribor | Triglav Cekada M.,Geodetski Institute Slovenije | Zalik B.,University of Maribor
Geodetski Vestnik | Year: 2013

This paper reviews two methods for digital terrain model generation from LiDAR data in test cases in Slovenia; both methods are based on concepts of mathematical morphology. A general overview of methods is given in the introduction, one of which is presented in more detail. The results show that both methods are able to correctly extract terrain points in more than 90% of the cases and are, therefore, suitable for usage even for such geographically diverse regions as Slovenia. Although the accuracy of both methods is comparable in cases of flat areas, the described method performs significantly better in problematic cases, such as hilly areas with relatively steep variable slopes, and terrains containing terraces. Even in these cases, the average absolute height error is not higher than 15 cm.


Aerial laser scanning (LIDAR) enables quick acquisition of terrain data and it can be used for the study of terrain under the vegetation. Therefore LIDAR is very appropriate for different geomorphologic studies. In this paper different characteristics of LIDAR are described, especially those which are important for decision, if LIDAR data are appropriate for the possible needs. The most important factors are the number of points per area unit (points/m 2) and the positional accuracy of the LIDAR data. On the example of landslides, rockfalls and different karst features the most suitable LIDAR data sets are defined. Based on the dimension of different geomorphologic features the number of LIDAR points per square meter will be defined. The largest landslides and different karst features can be studied with LIDAR data of 5 to 12 points/m 2. For medium extent landslides and smaller rockfalls the usage of more than 12 points/m 2 is recommended. For monitoring of more dynamic geomorphologic features, such as landslides, very accurate LIDAR data is needed. For static features, such as different karst features, only average LIDAR accuracy is needed.


Radovan D.,Geodetski Institute Slovenije
Geodetski Vestnik | Year: 2011

The geodetic profession provides geodetic data obtained in the fields of fundamental geodetic system, real estate and topography. Users integrate this data with other spatial data. The quality of such applications depends on the data quality; however, the providers and the users are not sufficiently aware of the cascading transfer of errors from the primary data layers to the secondary, derived data. Geodesy has traditionally considered errors mainly as positional errors, according to the law of the transfer of errors. Since the era of widespread digitizing of geodetic data began in the 1990s, data quality in the realm of geographic information systems has been expressed with the standardized parameters of data quality, and with metadata, of which positional accuracy is just one type. Unfortunately, in this way, the knowledge about which data is a reference can be obscured. To many users, it is not clear what is the specified quality referred to. This article describes, and intentionally uses, the term 'cascading', since for the rise of data quality one needs to upgrade data level by data level, starting first with the reference data and the semantic definitions of object types, and continuing by updating and harmonizing the secondary data, which were developed from the primary level. The reasons for the change of paradigm regarding the treatment of quality are considered. As the cascading poor quality of geodetic data can become a serious threat for the reputation of the profession of geodesy, several contemporary applications and projects are described in which this has already happened. In the conclusion, proposals are given for improving the situationion.


Cekada M.T.,Geodetski Institute Slovenije | Zorn M.,Geografski Institute Antona Melika | Kaufmann V.,University of Graz | Lieb G.K.,University of Graz
Geodetski Vestnik | Year: 2012

In the last century and a half, average summer temperatures have slowly been rising worldwide. The most observable consequence of this is the change in glacier sizes. For monitoring glacier area and volume, various measuring techniques exist-from measurements with a measuring tape and geodetic measurements to remote sensing and photogrammetry. A comparison of different measuring techniques on two Slovenian glaciers (the Triglav and Skuta glaciers) and two Austrian glaciers (the Gössnitzkees and Hornkees glaciers) is made. A long-term glacial retreat trend is presented for the Gössnitzkees, Hornkees, and Triglav glaciers because these glaciers can be monitored throughout the entire twentieth century by means of archival data. Despite their different sizes, the annual trend of glacial retreat was approximately the same in the period between 1929 and 2006.


A procedure of robust determination of the approximate coordinates of points in a horizontal geodetic network is presented. The primary aim is not accuracy but the reliability of the obtained coordinates. The motivation is to enable further processing according to the Gauss-Markov model. It is a linear mathematical model, thus the approximate values of unknowns are necessary input data. Disposable methods of determining coordinates of points and combinatorics of over-determined solutions dependent upon redundant observations are discussed. A geometrical approach is used, based on the fact that every point is an intersection of a pair of curves. The geometrical quality of each individual solution is evaluated from the intersection angle of both curves. A weight assigned to each solution is a function of that angle. Calculating coordinates is a successive procedure; each step assures the determination of one network point. The algorithm comprises searching for a typical solution among all solutions for an individual point. In order to avoid eventual gross errors, the procedure is based on robust statistics. The efficiency of three basic measures of location is tested on a practical example. The point is a generalization of mean, median, and mode i.e. the centre of mass, spatial median, and spatial mode. Gross errors are introduced into the network by using a Monte Carlo simulation.


Bric V.,Geodetski Institute Slovenije | Berk S.,Geodetski Institute Slovenije | Triglav Cekada M.,Geodetski Institute Slovenije
Geodetski Vestnik | Year: 2013

This paper deals with the problems of quality assurance for airborne laser-scanning data. Partial results of the project entitled 'Laser Scanning and Aerial Photographing of Slovenia 2011' are presented, and the quality control procedure is described. The focus is on the quality assurance of the geo-referencing used for water resource management. Important issues with an impact on the quality of data are addressed and evaluated. The quality of direct geo-referencing was investigated, and some experiences gained in the quality control of the project results are presented. The quality of the transformation of data into the national horizontal and height reference systems is also discussed. Some recommendations for the quality improvement of airborne laser-scanning data are given. This will be possible with the realisation of the new national height reference system and with the creation of the new geoid model.

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