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True orthophoto is a better product than a classical orthophoto in urban areas, because buildings are depicted in the correct plane position, and the content around the building is also visible. The main goal of our research was to verify two approaches of a true orthophoto production: a) true orthophoto production based on digital terrain model and digital building model, and b) automatic true orthophoto production. We performed the research in two test areas within the Municipality of Ljubljana. We compared the both procedures and the produced true orthophotos with the classical orthophoto, and assessed the production time component as well. To produce true orthophoto, larger overlapping of aerial images is required, thus the time for aerial surveying is increased by approximately 25 percentage. The time of manual work, compared to classical orthophoto production, is lower by the factor 0.27 for automatically produced true orthophoto, and is greater by the factor 2.75 for the true orthophoto based on digital terrain model and digital building model. Aesthetic appearance of automatically produced orthophoto has only minor shortcomings on the buildings’ roof edges which are slightly serrated. Considering all the mentioned aspects, the automatically produced true orthophoto is competitive with the classical orthophoto.

True orthophoto is a better product than a classical orthophoto in urban areas, because buildings are depicted in the correct plane position, and the content around the building is also visible. The main goal of our research was to verify two approaches of a true orthophoto production: a) true orthophoto production based on digital terrain model and digital building model, and b) automatic true orthophoto production. We performed the research in two test areas within the Municipality of Ljubljana. We compared the both procedures and the produced true orthophotos with the classical orthophoto, and assessed the production time component as well. To produce true orthophoto, larger overlapping of aerial images is required, thus the time for aerial surveying is increased by approximately 25 percentage. The time of manual work, compared to classical orthophoto production, is lower by the factor 0.27 for automatically produced true orthophoto, and is greater by the factor 2.75 for the true orthophoto based on digital terrain model and digital building model. Aesthetic appearance of automatically produced orthophoto has only minor shortcomings on the buildings’ roof edges which are slightly serrated. Considering all the mentioned aspects, the automatically produced true orthophoto is competitive with the classical orthophoto.

Unmanned aerial vehicles, equipped with various sensors and devices, are increasingly used to acquire geospatial data in geodesy, geoinformatics, and environmental studies. In this context, a new research and professional field has been developed – UAV photogrammetry – dealing with photogrammetry data acquisition and data processing, acquired by unmanned aerial vehicles. In this study, we analyse the selected factors that impact the quality of data provided using UAV photogrammetry, with the focus on positional accuracy; they are discussed in three groups: (a) factors related to the camera properties and the quality of images; (b) factors related to the mission planning and execution; and (c) factors related to the indirect georeferencing of images using ground control points. These selected factors are analysed based on the detailed review of relevant scientific publications. Additionally, the influence of the number of ground control points and their spatial distribution on point clouds' positional accuracy has been investigated for the case study. As the conclusion, key findings and recommendations for UAV photogrammetric projects are given; we have highlighted the importance of suitable lighting and weather conditions when performing UAV missions for spatial data acquisition, quality equipment, appropriate parameters of UAV data acquisition, and a sufficient number of ground control points, which should be determined with the appropriate positional accuracy and their correct distribution in the field.

Unmanned aerial vehicles, equipped with various sensors and devices, are increasingly used to acquire geospatial data in geodesy, geoinformatics, and environmental studies. In this context, a new research and professional field has been developed – UAV photogrammetry – dealing with photogrammetry data acquisition and data processing, acquired by unmanned aerial vehicles. In this study, we analyse the selected factors that impact the quality of data provided using UAV photogrammetry, with the focus on positional accuracy; they are discussed in three groups: (a) factors related to the camera properties and the quality of images; (b) factors related to the mission planning and execution; and (c) factors related to the indirect georeferencing of images using ground control points. These selected factors are analysed based on the detailed review of relevant scientific publications. Additionally, the influence of the number of ground control points and their spatial distribution on point clouds' positional accuracy has been investigated for the case study. As the conclusion, key findings and recommendations for UAV photogrammetric projects are given; we have highlighted the importance of suitable lighting and weather conditions when performing UAV missions for spatial data acquisition, quality equipment, appropriate parameters of UAV data acquisition, and a sufficient number of ground control points, which should be determined with the appropriate positional accuracy and their correct distribution in the field.

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.

The topic of this paper is the challenges of using remote sensing technologies as one of the potential data sources for the establishment of a 3D real property cadastre in Slovenia. More than a decade ago, the legal basis for the registration of property rights on the buildings and parts of buildings was provided in Slovenia, and for this purpose, the Building Cadastre was established. The analyses of the current data within the Land Cadastre and the Building Cadastre revealed that the 3D graphical representation of buildings, where the second level of detail (LoD 2) was discussed, requires additional data in which significant roof points should be additionally acquired. For this purpose, i.e. the creation of a graphical 3D-model of a building at the level LoD 2, we use the cadastral and national topographic data that covers the entire state territory, which are stereopairs of aerial photographs of the cyclic aerial survey (CAS) and airborne laser scanning data. Using a case study, we have analysed and discussed the appropriateness of the state airborne laser scanning data as an additional data source, along with the current cadastral data, for the creation of 3D-building model at the second level of detail, which is important from the cadastral as well as topographic perspective.

n this article, a method for the automatic detection of power lines in a horizontal xy plane from airborne and terrestrial laser scanning data is presented. The workflow is composed of four main steps: pre-processing with classification of a point cloud, filtering of the point cloud, the detection of points on the power lines by applying the Hough transform (HT), and vectorisation of power line locations and their intersections. In the pre-processing step, most of the points that are not representing power lines are eliminated via classification of the point cloud. We present our filter, which reduces the number of points in the point cloud further and thus accelerates data processing and increases the reliability of processing in the next steps. We detect the points on the power lines with the HT on the vector points in the xy plane. The final track of the power lines is derived from the straight segments computed by the method of the least squares from the points that HT recognised on the power lines. The results are assessed visually and via relative comparison of the computed intersections coordinates with the reference data manually extracted from the filtered point cloud. The proposed method detects almost all power lines in the test area for both data sets

A point cloud is the result of laser scanning; in the case of terrestrial laser scanning, the point cloud is composed of points scanned from one or more positions. To register these points into one point cloud, so-called tie points are needed; these may be object points (natural targets) or selected stabilized targets (artificial targets). Spherical targets are often used as artificial targets; these must have their centre coordinates and radius determined. The centre coordinates of a sphere are calculated on the basis of scanned points on the spheres’ surface. This paper presents two procedures for determining the best reflection region on the sphere to determine its parameters, and the procedure for determining the optimal distance between the scanner and sphere.The best reflection area on the sphere is determined in two ways. The first is based on minimizing the difference between sphere radii when, in the adjustment process, the radius of the sphere is treated as a known and unknown quantity. The second is based on the standard deviation of the sphere’s centre coordinates at the independent determinations of sphere parameters from randomly chosen scanned points on the sphere surface. For each of the spheres, the best ratio between the laser beam footprint area and the target surface area is calculated for the optimal combination of scanning distance and region. For the best combination of scanning distance and region, we chose the one with the smallest standard deviation of the sphere centre coordinates.

The update of topographic databases is an important task fir organizations that maintain them. Building data are one of the important data types in topographic databases. The article describes a method for automatic building extraction from digital surface model and multispectral orthophoto and the use of extraction results for the building change detection in the topographic database. The initial building mask was created from the normalized digital surface model (nDSM). Vegetation was eliminated from the building mask using a modified vegetation index calculated from the infrared orthophoto and also considering the shadow index and the nDMP texture. The final building mask was vectorised using Radon transform, The results of the automatic building extraction were compared to the building cadastre and the actual situation on the ground. The automatic method detected 94.4% of all buildings in the area. We concluded that the described method is appropriate for capturing of the building data for the topographic database in scales 1: 10 000 and smaller. Automatic change detection results (completeness 93.5% and correctness 78.4%) indicate that the described method is appropriate for building change detection.

Topografski podatki, kot pomemben del Nacionalne prostorske podatkovne infrastrukture, so bili v letih po osamosvojitvi Slovenije deležni velike pozornosti, postali so splošno dostopni, bili so dopolnjeni in medsebojno usklajeni. V zadnjem desetletju pa se je vlaganje v topografske podatke v Sloveniji zelo omejilo, zato danes nikakor več ne moremo biti zadovoljni z njihovim stanjem. V prispevku pregledno predstavljamo stanje topografskih podatkov v Sloveniji, analiziramo njihovo kakovost in ustreznost za potencialne in dejanske uporabnike. Posvetimo se izvornim posnetkom stanja, kot je sistemsko ciklično aerosnemanje (CAS), in iz njega izvedenemu proizvodu, ortofotu. Kakovost ortofota je precej odvisna od kakovosti modela reliefa. Topografski podatki so vodeni posamično v sklopu posameznih vsebinskih baz (REZI, ZK GJI, grafični del katastra stavb) ter združeno v topografskih bazah in kartah različnih ravni podrobnosti (DTK 5, DTK 25, DTK 50, sistem DPK). Analizirano stanje primerjamo s stanjem v nekaterih sosednjih ali primerljivih državah ; Topographic data, an important part of the National Spatial Data Infrastructure, have been given serious attention since Slovenia’s independence. It has become publicly available, updated and harmonised. Financing of topographic data in Slovenia has significantly decreased over the previous decade. As a result, the present status is far from acceptable or expected. The current status of the topographic data, as well as its quality and usability for potential users is discussed in this article. The overview starts with basic source data, aerial surveys, photographs and orthophotos. The quality of orthophotos largely depends on the DTM quality. Topographic data is nowadays organised in thematic datasets (geographical names, building cadastre, etc.) or joined in datasets of different levels of accuracy and details. The status in Slovenia is compared to those in some neighbouring and other comparable countries.

Topographic data, an important part of the National Spatial Data Infrastructure, have been given serious attention since Slovenia's independence. It has become publicly available, updated and harmonised. Financing of topographic data in Slovenia has significantly decreased over the previous decade. As a result, the present status is far from acceptable or expected. The current status of the topographic data, as well as its quality and usability for potential users is discussed in this article. The overview starts with basic source data, aerial surveys, photographs and orthophotos. The quality of orthophotos largely depends on the DTM quality. Topographic data is nowadays organised in thematic datasets (geographical names, building cadastre, etc.) or joined in datasets of different levels of accuracy and details. The status in Slovenia is compared to those in some neighbouring and other comparable countries.

When ordering LiDAR data, LiDAR point density per surface unit is important information with decisive influence on the price of the LiDAR survey. The paper first deals with the theoretical calculation of the minimum LiDAR point density, necessary for the acquisition of topographic data of the largest scales. For this purpose the sampling theorem is used. However, since topographic objects (roads, water bodies, etc.) and phenomena represented on topographic maps and in topographic bases are in many cases located under vegetation, also the rate of laser beam penetration through vegetation for thearea where the topographic data are to be gathered has to be known. In a research on a test case conducted in the area of the town Nova Gorica we calculated the rate of laser beam penetration for four different vegetation types: scarce Mediterranean vegetation,thick thermophilic deciduous forest, mixed vegetation (meadows, orchards and forest) and built-up area. By connecting the theoretic minimum LiDAR point density with the rate of penetration, we defined the minimum LiDAR point density for the needs of data acquisition on topographic maps of the largest scales or in topographic bases of comparable detail (from 1 : 1000 to 1 : 10,000).

In the paper the results of the research on the complete automation of the relative orientation of a stereo pair is presented. The theoretical background needed for understanding this topic is described and the results of testing the algorithms with real data are presented. In general, the relative orientation procedure consists of three phases: input data acquisition, computation ofrelative orientation parameters and estimation of observation errors. In the process of the complete relative orientation automation, the key step is the automation of homologous points acquisition in the stereo area. In the tests presented, the homologous points were acquired with different methods: manually, semiautomatically and fully automatically. The results ofthe computed relative orientation parameters have been compared. It has been concluded that the automation of the relative orientation procedure is successful and reliable if the control of the observation errors estimation is built into the procedure, and,especially, we get the results faster than with the manual or semi-automated method.

Airborne laser scanning of a terrain results, in addition to polar coordinate measurements, in intensity measurement of the reflected laser beam. Because the 3D lidar point cloud itself does not include information about the object types on which points are located,intensity measurements provide the important data for identification of objects and phenomena in the physical space. This is confirmed by the colour coded intensity value image, where particular objects (asphalt road, grass, building etc.) can be recognized. The measuredintensity values have been analyzed within the Neusiedler See project case, part of a transnational project SISTEMaPARC (Interreg IIIB). We have investigated the land use classes that could bedifferentiated on the basis of intensity values thus enabling the land use classification.

Vzdrževanje podatkov v topografskih bazah je ena od pomembnejših nalog organizacij, ki te podatkovne baze vodijo. Eden od pomembnih podatkovnih slojev v topografskih bazah so podatki o stavbah. V člankusta opisani metoda za samodejen zajem stavb iz digitalnega modela površja in multispektralnega ortofota ter uporaba rezultatov zajema za samodejno iskanje sprememb v topografskih bazah, v katerih se vodijo podatki o stavbah. Začetno masko stavb smo izdelali iz normaliziranega digitalnega modela površja (nDMP). Vegetacijo smo iz maske stavb izločili z modificiranim vegetacijskim indeksom, izračunanim iz infrardečega ortofota ob upoštevanju indeksa senc in teksture nDMP. Na končni maski smo stavbe vektorizirali z uporabo transformacije Radon. Rezultate samodejnega zajema stavb smo primerjali s katastrom stavb in dejanskim stanjem na terenu. Ssamodejnim postopkom smo našli 94,4 % vseh stavb na območju in ocenili, da je opisana metoda primerna za zajem podatkov o stavbah za topografske baze v merilih 1 : 10 000 in manj. Rezultat samodejnegaiskanja sprememb (popolnost 93,5 % in pravilnost 78,4 %) kaže, da je opisana metoda primerna za iskanje sprememb med podatki o stavbah ; The update of topographic databases is an important task for organizations that maintain them. Building data are one of the important data types in topographic databases. The article describes a method for automatic building extraction from digital surfacemodel and multispectral orthophoto and the use of extraction results for the building change detection in the topographic database. The initial building mask was created from the normalized digital surface model (nDSM).Vegetation was eliminated from the building mask using a modified vegetation index calculated from the infrared orthophoto and also considering the shadow index and the nDMP texture. The finalbuilding mask was vectorised using Radon transform. The results of the automatic building extraction were compared to the building cadastre and the actual situation on the ground. The automatic methoddetected 94.4% of all buildings in the area. We concluded that the described method is appropriate for capturing of the building data for the topographic database in scales 1 : 10 000 and smaller. Automatic change detection results (completeness 93.5% and correctness 78.4%) indicate that the described method is appropriate for building change detection.